diff --git a/PROMPT.md b/PROMPT.md
index b1bd27e..6a01f10 100644
--- a/PROMPT.md
+++ b/PROMPT.md
@@ -24,7 +24,7 @@ Device Discovery
 
 Partitioning Requirements
 - Use GPT exclusively. Honor 1 MiB alignment boundaries.
-- For BIOS compatibility, create a small `bios_boot` partition (exact size TBD—assume 1 MiB for now, placed first).
+- For BIOS compatibility on BIOS systems, create a small `bios_boot` partition (size 1 MiB, placed first). When running under UEFI (`/sys/firmware/efi` present), the BIOS boot partition is suppressed.
 - Create a 512 MiB FAT32 ESP on each disk, label `ZOSBOOT`. Each ESP is independent; synchronization will be handled by another tool (out of scope). Ensure unique partition UUIDs while keeping identical labels.
 - Remaining disk capacity is provisioned per configuration (see below).
 - Before making changes, verify the device has no existing partitions or filesystem signatures; abort otherwise.
@@ -51,11 +51,11 @@ Filesystem Provisioning
 
 Configuration Input
 - Accept configuration via:
-  * Kernel command line parameter (name TBD, e.g., `zosstorage.config=`) pointing to a YAML configuration descriptor.
-  * Optional CLI flags when run in user space (must mirror kernel cmdline semantics).
-  * On-disk YAML config file (default path TBD, e.g., `/etc/zosstorage/config.yaml`).
-- Establish clear precedence: kernel cmdline overrides CLI arguments, which override config file defaults. No interactive prompts inside initramfs.
-- YAML schema must at least describe disk selection rules, desired filesystem layout, boot partition preferences, filesystem options, mount targets, and logging verbosity. Document the schema and provide validation.
+  * Kernel command line parameter `zosstorage.config=` pointing to a YAML configuration descriptor.
+  * Optional CLI flags when run in user space (mirror kernel cmdline semantics).
+  * On-disk YAML config file (default path `/etc/zosstorage/config.yaml`).
+- Precedence: kernel cmdline overrides CLI arguments, which override config file, which override built-in defaults. No interactive prompts inside initramfs.
+- YAML schema must describe disk selection rules, desired filesystem layout, boot partition preferences, filesystem options, mount targets, and logging verbosity. See [docs/SCHEMA.md](docs/SCHEMA.md) and [src/types.rs](src/types.rs:1).
 
 State Reporting
 - After successful provisioning, emit a JSON state report (path TBD, e.g., `/run/zosstorage/state.json`) capturing:
@@ -70,7 +70,7 @@ Logging
 - By default, logs go to stderr; design for optional redirection to a file (path TBD). Avoid using `println!`.
 
 System Integration
-- Decide whether to generate `/etc/fstab` entries; if enabled, produce deterministic ordering and documentation. Otherwise, document alternative mount management.
+- `/etc/fstab` generation: optional via CLI/config. When enabled, write only the four final subvolume/subdir mount entries (system, etc, modules, vm-meta) with `UUID=` sources in deterministic order. Root mounts under `/var/mounts/{UUID}` are runtime-only and excluded from fstab.
 - After provisioning, ensure the initramfs can mount the new filesystems (e.g., call `udevadm settle` if necessary). No external services are invoked.
 - No responsibility for updating `vmlinuz.efi`; another subsystem handles kernel updates.
 
@@ -95,11 +95,17 @@ Documentation & Deliverables
 - Include architectural notes describing module boundaries (device discovery, partitioning, filesystem provisioning, config parsing, logging, reporting).
 
 Open Items (call out explicitly)
-- Exact sizes and ordering for `bios_boot` partition awaiting confirmation; note assumptions in code and documentation.
-- Mount point naming scheme under `/var/cache` (per-UUID vs. config-defined) still to be finalized.
-- Filesystem-specific tuning parameters (compression, RAID values, `bcachefs` options) require explicit defaults from stakeholders.
-- Path/location for YAML config, kernel cmdline key, JSON report path, and optional log file path need final confirmation.
-- Decision whether `/etc/fstab` is generated remains pending.
+- BIOS vs UEFI: `bios_boot` partition size fixed at 1 MiB and created only on BIOS systems; suppressed under UEFI (`/sys/firmware/efi` present).
+- Mount scheme finalized:
+  - Root mounts for each data filesystem at `/var/mounts/{UUID}` (runtime only).
+  - Final subvolume/subdir mounts from the primary data filesystem to `/var/cache/{system,etc,modules,vm-meta}`.
+- Filesystem-specific tuning parameters (compression, RAID values, `bcachefs` options) remain open for refinement; sensible defaults applied.
+- Config paths and keys stabilized:
+  - Kernel cmdline key: `zosstorage.config=`
+  - Default config file: `/etc/zosstorage/config.yaml`
+  - Default report path: `/run/zosstorage/state.json`
+  - Optional log file: `/run/zosstorage/zosstorage.log`
+- `/etc/fstab` generation policy decided: optional flag; writes only the four final subvolume/subdir entries.
 
 Implementation Constraints
 - Stick to clear module boundaries. Provide unit tests where possible (e.g., config parsing, device filtering).
diff --git a/README.md b/README.md
index a159668..1f84a3e 100644
--- a/README.md
+++ b/README.md
@@ -2,7 +2,7 @@
 
 One-shot disk provisioning utility intended for initramfs. It discovers eligible disks, plans a GPT layout based on a chosen topology, creates filesystems, mounts them under a predictable scheme, and emits a machine-readable report. Safe-by-default with a non-destructive preview mode.
 
-Status: first-draft preview capable. Partition apply, mkfs, and mounts are gated until the planning is validated in your environment.
+Status: apply mode implemented. Partition application (sgdisk), filesystem creation (vfat/btrfs/bcachefs), mount scheme with subvolumes, and optional fstab writing are available. Preview mode remains supported.
 
 Key modules
 - CLI and entrypoint:
@@ -33,8 +33,9 @@ Requirements
 - Linux with /proc and /sys mounted (initramfs friendly)
 - External tools discovered at runtime:
   - blkid (for probing UUIDs and signatures)
-  - sgdisk (for GPT application) — planned
-  - mkfs.vfat, mkfs.btrfs, bcachefs (for formatting) — invoked by fs/plan when enabled in execution phase
+  - sgdisk (for GPT application)
+  - mkfs.vfat, mkfs.btrfs, bcachefs (for formatting)
+  - udevadm (optional; for settle after partitioning)
 - Tracing/logging to stderr by default; optional file at /run/zosstorage/zosstorage.log
 
 Install and build
@@ -57,6 +58,7 @@ CLI usage
 - Other:
   -c, --config PATH           Merge a YAML config file (overrides defaults)
   -s, --fstab                 Enable writing /etc/fstab entries (when mounts are applied)
+  -a, --apply                 Perform partitioning, filesystem creation, and mounts (destructive)
   -f, --force                 Present but not implemented (returns an error)
 
 Examples
@@ -68,6 +70,8 @@ Examples
   sudo ./zosstorage --show -t ssd-hdd-bcachefs --allow-removable -l debug
 - Quiet plan to file:
   sudo ./zosstorage --report /run/zosstorage/plan.json -t dual-independent
+- Apply single-disk btrfs (DESTRUCTIVE; wipes target disk):
+  sudo ./zosstorage --apply -t btrfs-single
 
 Preview JSON shape (examples)
 1) Already provisioned (idempotency success):
@@ -107,14 +111,15 @@ Preview JSON shape (examples)
     }
   ],
   "filesystems_planned": [
-    { "kind": "vfat", "from_roles": ["esp"], "label": "ZOSBOOT", "planned_mountpoint": null },
-    { "kind": "btrfs", "from_roles": ["data"], "devices_planned": 2, "label": "ZOSDATA", "planned_mountpoint_template": "/var/cache/{UUID}" }
+    { "kind": "vfat", "from_roles": ["esp"], "label": "ZOSBOOT" },
+    { "kind": "btrfs", "from_roles": ["data"], "devices_planned": 2, "label": "ZOSDATA" }
   ],
   "mount": {
     "scheme": "per_uuid",
     "base_dir": "/var/cache",
     "fstab_enabled": false,
-    "target_template": "/var/cache/{UUID}"
+    "root_mount_template": "/var/mounts/{UUID}",
+    "final_targets": ["/var/cache/system", "/var/cache/etc", "/var/cache/modules", "/var/cache/vm-meta"]
   }
 }
 
diff --git a/docs/API-SKELETONS.md b/docs/API-SKELETONS.md
index e325c86..a3d8b1f 100644
--- a/docs/API-SKELETONS.md
+++ b/docs/API-SKELETONS.md
@@ -6,34 +6,34 @@ Purpose
 - After approval, these will be created in the src tree in Code mode.
 
 Index
-- [src/lib.rs](src/lib.rs)
-- [src/errors.rs](src/errors.rs)
-- [src/main.rs](src/main.rs)
-- [src/cli/args.rs](src/cli/args.rs)
-- [src/logging/mod.rs](src/logging/mod.rs)
-- [src/types.rs](src/types.rs)
-- [src/config/loader.rs](src/config/loader.rs)
-- [src/device/discovery.rs](src/device/discovery.rs)
-- [src/partition/plan.rs](src/partition/plan.rs)
-- [src/fs/plan.rs](src/fs/plan.rs)
-- [src/mount/ops.rs](src/mount/ops.rs)
-- [src/report/state.rs](src/report/state.rs)
-- [src/orchestrator/run.rs](src/orchestrator/run.rs)
-- [src/idempotency/mod.rs](src/idempotency/mod.rs)
-- [src/util/mod.rs](src/util/mod.rs)
+- [src/lib.rs](../src/lib.rs)
+- [src/errors.rs](../src/errors.rs)
+- [src/main.rs](../src/main.rs)
+- [src/cli/args.rs](../src/cli/args.rs)
+- [src/logging/mod.rs](../src/logging/mod.rs)
+- [src/types.rs](../src/types.rs)
+- [src/config/loader.rs](../src/config/loader.rs)
+- [src/device/discovery.rs](../src/device/discovery.rs)
+- [src/partition/plan.rs](../src/partition/plan.rs)
+- [src/fs/plan.rs](../src/fs/plan.rs)
+- [src/mount/ops.rs](../src/mount/ops.rs)
+- [src/report/state.rs](../src/report/state.rs)
+- [src/orchestrator/run.rs](../src/orchestrator/run.rs)
+- [src/idempotency/mod.rs](../src/idempotency/mod.rs)
+- [src/util/mod.rs](../src/util/mod.rs)
 
 Conventions
-- Shared [type Result<T>](src/errors.rs:1) and [enum Error](src/errors.rs:1).
+- Shared [type Result<T>](../src/errors.rs:1) and [enum Error](../src/errors.rs:1).
 - No stdout prints; use tracing only.
-- External tools invoked via [util](src/util/mod.rs) wrappers.
+- External tools invoked via [util](../src/util/mod.rs) wrappers.
 
 ---
 
 ## Crate root
 
 References
-- [src/lib.rs](src/lib.rs)
-- [type Result<T> = std::result::Result<T, Error>](src/errors.rs:1)
+- [src/lib.rs](../src/lib.rs)
+- [type Result<T> = std::result::Result<T, Error>](../src/errors.rs:1)
 
 Skeleton (for later implementation in code mode)
 ```rust
@@ -63,8 +63,8 @@ pub const VERSION: &str = env!("CARGO_PKG_VERSION");
 ## Errors
 
 References
-- [enum Error](src/errors.rs:1)
-- [type Result<T>](src/errors.rs:1)
+- [enum Error](../src/errors.rs:1)
+- [type Result<T>](../src/errors.rs:1)
 
 Skeleton
 ```rust
@@ -107,8 +107,8 @@ pub type Result<T> = std::result::Result<T, Error>;
 ## Entrypoint
 
 References
-- [fn main()](src/main.rs:1)
-- [fn run(ctx: &Context) -> Result<()>](src/orchestrator/run.rs:1)
+- [fn main()](../src/main.rs:1)
+- [fn run(ctx: &Context) -> Result<()>](../src/orchestrator/run.rs:1)
 
 Skeleton
 ```rust
@@ -143,8 +143,8 @@ fn real_main() -> Result<()> {
 ## CLI
 
 References
-- [struct Cli](src/cli/args.rs:1)
-- [fn from_args() -> Cli](src/cli/args.rs:1)
+- [struct Cli](../src/cli/args.rs:1)
+- [fn from_args() -> Cli](../src/cli/args.rs:1)
 
 Skeleton
 ```rust
@@ -170,6 +170,18 @@ pub struct Cli {
     #[arg(long = "fstab", default_value_t = false)]
     pub fstab: bool,
 
+    /// Print preview JSON to stdout (non-destructive)
+    #[arg(long = "show", default_value_t = false)]
+    pub show: bool,
+
+    /// Write preview JSON to a file (non-destructive)
+    #[arg(long = "report")]
+    pub report: Option<String>,
+
+    /// Perform partitioning, filesystem creation, and mounts (DESTRUCTIVE)
+    #[arg(long = "apply", default_value_t = false)]
+    pub apply: bool,
+
     /// Present but non-functional; returns unimplemented error
     #[arg(long = "force")]
     pub force: bool,
@@ -186,8 +198,8 @@ pub fn from_args() -> Cli {
 ## Logging
 
 References
-- [struct LogOptions](src/logging/mod.rs:1)
-- [fn init_logging(opts: &LogOptions) -> Result<()>](src/logging/mod.rs:1)
+- [struct LogOptions](../src/logging/mod.rs:1)
+- [fn init_logging(opts: &LogOptions) -> Result<()>](../src/logging/mod.rs:1)
 
 Skeleton
 ```rust
@@ -218,13 +230,13 @@ pub fn init_logging(opts: &LogOptions) -> Result<()> {
 ## Configuration types
 
 References
-- [struct Config](src/types.rs:1)
-- [enum Topology](src/types.rs:1)
-- [struct DeviceSelection](src/types.rs:1)
-- [struct Partitioning](src/types.rs:1)
-- [struct FsOptions](src/types.rs:1)
-- [struct MountScheme](src/types.rs:1)
-- [struct ReportOptions](src/types.rs:1)
+- [struct Config](../src/types.rs:1)
+- [enum Topology](../src/types.rs:1)
+- [struct DeviceSelection](../src/types.rs:1)
+- [struct Partitioning](../src/types.rs:1)
+- [struct FsOptions](../src/types.rs:1)
+- [struct MountScheme](../src/types.rs:1)
+- [struct ReportOptions](../src/types.rs:1)
 
 Skeleton
 ```rust
@@ -247,8 +259,10 @@ pub struct DeviceSelection {
 #[derive(Debug, Clone, Serialize, Deserialize)]
 #[serde(rename_all = "snake_case")]
 pub enum Topology {
-    Single,
+    BtrfsSingle,
+    BcachefsSingle,
     DualIndependent,
+    Bcachefs2Copy,
     SsdHddBcachefs,
     BtrfsRaid1,
 }
@@ -351,8 +365,8 @@ pub struct Config {
 ## Configuration I/O
 
 References
-- [fn load_and_merge(cli: &Cli) -> Result<Config>](src/config/loader.rs:1)
-- [fn validate(cfg: &Config) -> Result<()>](src/config/loader.rs:1)
+- [fn load_and_merge(cli: &Cli) -> Result<Config>](../src/config/loader.rs:1)
+- [fn validate(cfg: &Config) -> Result<()>](../src/config/loader.rs:1)
 
 Skeleton
 ```rust
@@ -374,10 +388,10 @@ pub fn validate(cfg: &crate::config::types::Config) -> Result<()> {
 ## Device discovery
 
 References
-- [struct Disk](src/device/discovery.rs:1)
-- [struct DeviceFilter](src/device/discovery.rs:1)
-- [trait DeviceProvider](src/device/discovery.rs:1)
-- [fn discover(filter: &DeviceFilter) -> Result<Vec<Disk>>](src/device/discovery.rs:1)
+- [struct Disk](../src/device/discovery.rs:1)
+- [struct DeviceFilter](../src/device/discovery.rs:1)
+- [trait DeviceProvider](../src/device/discovery.rs:1)
+- [fn discover(filter: &DeviceFilter) -> Result<Vec<Disk>>](../src/device/discovery.rs:1)
 
 Skeleton
 ```rust
@@ -418,12 +432,12 @@ pub fn discover(filter: &DeviceFilter) -> Result<Vec<Disk>> {
 ## Partitioning
 
 References
-- [enum PartRole](src/partition/plan.rs:1)
-- [struct PartitionSpec](src/partition/plan.rs:1)
-- [struct PartitionPlan](src/partition/plan.rs:1)
-- [struct PartitionResult](src/partition/plan.rs:1)
-- [fn plan_partitions(disks: &[Disk], cfg: &Config) -> Result<PartitionPlan>](src/partition/plan.rs:1)
-- [fn apply_partitions(plan: &PartitionPlan) -> Result<Vec<PartitionResult>>](src/partition/plan.rs:1)
+- [enum PartRole](../src/partition/plan.rs:1)
+- [struct PartitionSpec](../src/partition/plan.rs:1)
+- [struct PartitionPlan](../src/partition/plan.rs:1)
+- [struct PartitionResult](../src/partition/plan.rs:1)
+- [fn plan_partitions(disks: &[Disk], cfg: &Config) -> Result<PartitionPlan>](../src/partition/plan.rs:1)
+- [fn apply_partitions(plan: &PartitionPlan) -> Result<Vec<PartitionResult>>](../src/partition/plan.rs:1)
 
 Skeleton
 ```rust
@@ -485,12 +499,12 @@ pub fn apply_partitions(plan: &PartitionPlan) -> Result<Vec<PartitionResult>> {
 ## Filesystems
 
 References
-- [enum FsKind](src/fs/plan.rs:1)
-- [struct FsSpec](src/fs/plan.rs:1)
-- [struct FsPlan](src/fs/plan.rs:1)
-- [struct FsResult](src/fs/plan.rs:1)
-- [fn plan_filesystems(...)](src/fs/plan.rs:1)
-- [fn make_filesystems(...)](src/fs/plan.rs:1)
+- [enum FsKind](../src/fs/plan.rs:1)
+- [struct FsSpec](../src/fs/plan.rs:1)
+- [struct FsPlan](../src/fs/plan.rs:1)
+- [struct FsResult](../src/fs/plan.rs:1)
+- [fn plan_filesystems(...)](../src/fs/plan.rs:1)
+- [fn make_filesystems(...)](../src/fs/plan.rs:1)
 
 Skeleton
 ```rust
@@ -531,8 +545,8 @@ pub fn plan_filesystems(
     todo!("map ESP to vfat, data to btrfs or bcachefs according to topology")
 }
 
-/// Create the filesystems and return identity info (UUIDs, labels).
-pub fn make_filesystems(plan: &FsPlan) -> Result<Vec<FsResult>> {
+//// Create the filesystems and return identity info (UUIDs, labels).
+pub fn make_filesystems(plan: &FsPlan, cfg: &Config) -> Result<Vec<FsResult>> {
     todo!("invoke mkfs tools with configured options via util::run_cmd")
 }
 ```
@@ -542,11 +556,11 @@ pub fn make_filesystems(plan: &FsPlan) -> Result<Vec<FsResult>> {
 ## Mounting
 
 References
-- [struct MountPlan](src/mount/ops.rs:1)
-- [struct MountResult](src/mount/ops.rs:1)
-- [fn plan_mounts(...)](src/mount/ops.rs:1)
-- [fn apply_mounts(...)](src/mount/ops.rs:1)
-- [fn maybe_write_fstab(...)](src/mount/ops.rs:1)
+- [struct MountPlan](../src/mount/ops.rs:1)
+- [struct MountResult](../src/mount/ops.rs:1)
+- [fn plan_mounts(...)](../src/mount/ops.rs:1)
+- [fn apply_mounts(...)](../src/mount/ops.rs:1)
+- [fn maybe_write_fstab(...)](../src/mount/ops.rs:1)
 
 Skeleton
 ```rust
@@ -565,9 +579,13 @@ pub struct MountResult {
     pub options: String,
 }
 
-/// Build mount plan under /var/cache/<UUID> by default.
+//// Build mount plan:
+//// - Root-mount all data filesystems under `/var/mounts/{UUID}` (runtime only)
+//// - Ensure/create subvolumes on the primary data filesystem: system, etc, modules, vm-meta
+//// - Plan final mounts to `/var/cache/{system,etc,modules,vm-meta}` using
+////   `subvol=` for btrfs and `X-mount.subdir=` for bcachefs.
 pub fn plan_mounts(fs_results: &[FsResult], cfg: &Config) -> Result<MountPlan> {
-    todo!("create per-UUID directories and mount mapping")
+    todo!("root mounts under /var/mounts/{UUID}; final subvol/subdir mounts to /var/cache/{system,etc,modules,vm-meta}")
 }
 
 /// Apply mounts using syscalls (nix), ensuring directories exist.
@@ -575,9 +593,12 @@ pub fn apply_mounts(plan: &MountPlan) -> Result<Vec<MountResult>> {
     todo!("perform mount syscalls and return results")
 }
 
-/// Optionally generate /etc/fstab entries in deterministic order.
+//// Optionally generate /etc/fstab entries for final subvolume/subdir mounts only.
+//// - Write exactly four entries: system, etc, modules, vm-meta
+//// - Use UUID= sources; deterministic order by target path
+//// - Exclude runtime root mounts under `/var/mounts/{UUID}`
 pub fn maybe_write_fstab(mounts: &[MountResult], cfg: &Config) -> Result<()> {
-    todo!("when enabled, write fstab entries")
+    todo!("when enabled, write only the four final subvolume/subdir entries with UUID= sources")
 }
 ```
 
@@ -586,10 +607,10 @@ pub fn maybe_write_fstab(mounts: &[MountResult], cfg: &Config) -> Result<()> {
 ## Reporting
 
 References
-- [const REPORT_VERSION: &str](src/report/state.rs:1)
-- [struct StateReport](src/report/state.rs:1)
-- [fn build_report(...)](src/report/state.rs:1)
-- [fn write_report(...)](src/report/state.rs:1)
+- [const REPORT_VERSION: &str](../src/report/state.rs:1)
+- [struct StateReport](../src/report/state.rs:1)
+- [fn build_report(...)](../src/report/state.rs:1)
+- [fn write_report(...)](../src/report/state.rs:1)
 
 Skeleton
 ```rust
@@ -632,8 +653,8 @@ pub fn write_report(report: &StateReport, path: &str) -> Result<()> {
 ## Orchestrator
 
 References
-- [struct Context](src/orchestrator/run.rs:1)
-- [fn run(ctx: &Context) -> Result<()>](src/orchestrator/run.rs:1)
+- [struct Context](../src/orchestrator/run.rs:1)
+- [fn run(ctx: &Context) -> Result<()>](../src/orchestrator/run.rs:1)
 
 Skeleton
 ```rust
@@ -662,8 +683,8 @@ pub fn run(ctx: &Context) -> Result<()> {
 ## Idempotency
 
 References
-- [fn detect_existing_state() -> Result<Option<StateReport>>](src/idempotency/mod.rs:1)
-- [fn is_empty_disk(disk: &Disk) -> Result<bool>](src/idempotency/mod.rs:1)
+- [fn detect_existing_state() -> Result<Option<StateReport>>](../src/idempotency/mod.rs:1)
+- [fn is_empty_disk(disk: &Disk) -> Result<bool>](../src/idempotency/mod.rs:1)
 
 Skeleton
 ```rust
@@ -685,11 +706,11 @@ pub fn is_empty_disk(disk: &Disk) -> Result<bool> {
 ## Utilities
 
 References
-- [struct CmdOutput](src/util/mod.rs:1)
-- [fn which_tool(name: &str) -> Result<Option<String>>](src/util/mod.rs:1)
-- [fn run_cmd(args: &[&str]) -> Result<()>](src/util/mod.rs:1)
-- [fn run_cmd_capture(args: &[&str]) -> Result<CmdOutput>](src/util/mod.rs:1)
-- [fn udev_settle(timeout_ms: u64) -> Result<()>](src/util/mod.rs:1)
+- [struct CmdOutput](../src/util/mod.rs:1)
+- [fn which_tool(name: &str) -> Result<Option<String>>](../src/util/mod.rs:1)
+- [fn run_cmd(args: &[&str]) -> Result<()>](../src/util/mod.rs:1)
+- [fn run_cmd_capture(args: &[&str]) -> Result<CmdOutput>](../src/util/mod.rs:1)
+- [fn udev_settle(timeout_ms: u64) -> Result<()>](../src/util/mod.rs:1)
 
 Skeleton
 ```rust
@@ -722,6 +743,11 @@ pub fn run_cmd_capture(args: &[&str]) -> Result<CmdOutput> {
 pub fn udev_settle(timeout_ms: u64) -> Result<()> {
     todo!("invoke udevadm settle when present")
 }
+
+/// Detect UEFI environment by checking /sys/firmware/efi; used to suppress BIOS boot partition on UEFI.
+pub fn is_efi_boot() -> bool {
+    todo!("return Path::new(\"/sys/firmware/efi\").exists()")
+}
 ```
 
 ---
@@ -735,24 +761,24 @@ Approval gate
   - Add initial tests scaffolding and example configs.
 
 References summary
-- [fn main()](src/main.rs:1)
-- [fn from_args()](src/cli/args.rs:1)
-- [fn init_logging(opts: &LogOptions)](src/logging/mod.rs:1)
-- [fn load_and_merge(cli: &Cli)](src/config/loader.rs:1)
-- [fn validate(cfg: &Config)](src/config/loader.rs:1)
-- [fn discover(filter: &DeviceFilter)](src/device/discovery.rs:1)
-- [fn plan_partitions(disks: &[Disk], cfg: &Config)](src/partition/plan.rs:1)
-- [fn apply_partitions(plan: &PartitionPlan)](src/partition/plan.rs:1)
-- [fn plan_filesystems(parts: &[PartitionResult], cfg: &Config)](src/fs/plan.rs:1)
-- [fn make_filesystems(plan: &FsPlan)](src/fs/plan.rs:1)
-- [fn plan_mounts(fs_results: &[FsResult], cfg: &Config)](src/mount/ops.rs:1)
-- [fn apply_mounts(plan: &MountPlan)](src/mount/ops.rs:1)
-- [fn maybe_write_fstab(mounts: &[MountResult], cfg: &Config)](src/mount/ops.rs:1)
-- [fn build_report(...)](src/report/state.rs:1)
-- [fn write_report(report: &StateReport)](src/report/state.rs:1)
-- [fn detect_existing_state()](src/idempotency/mod.rs:1)
-- [fn is_empty_disk(disk: &Disk)](src/idempotency/mod.rs:1)
-- [fn which_tool(name: &str)](src/util/mod.rs:1)
-- [fn run_cmd(args: &[&str])](src/util/mod.rs:1)
-- [fn run_cmd_capture(args: &[&str])](src/util/mod.rs:1)
-- [fn udev_settle(timeout_ms: u64)](src/util/mod.rs:1)
\ No newline at end of file
+- [fn main()](../src/main.rs:1)
+- [fn from_args()](../src/cli/args.rs:1)
+- [fn init_logging(opts: &LogOptions)](../src/logging/mod.rs:1)
+- [fn load_and_merge(cli: &Cli)](../src/config/loader.rs:1)
+- [fn validate(cfg: &Config)](../src/config/loader.rs:1)
+- [fn discover(filter: &DeviceFilter)](../src/device/discovery.rs:1)
+- [fn plan_partitions(disks: &[Disk], cfg: &Config)](../src/partition/plan.rs:1)
+- [fn apply_partitions(plan: &PartitionPlan)](../src/partition/plan.rs:1)
+- [fn plan_filesystems(parts: &[PartitionResult], cfg: &Config)](../src/fs/plan.rs:1)
+- [fn make_filesystems(plan: &FsPlan)](../src/fs/plan.rs:1)
+- [fn plan_mounts(fs_results: &[FsResult], cfg: &Config)](../src/mount/ops.rs:1)
+- [fn apply_mounts(plan: &MountPlan)](../src/mount/ops.rs:1)
+- [fn maybe_write_fstab(mounts: &[MountResult], cfg: &Config)](../src/mount/ops.rs:1)
+- [fn build_report(...)](../src/report/state.rs:1)
+- [fn write_report(report: &StateReport)](../src/report/state.rs:1)
+- [fn detect_existing_state()](../src/idempotency/mod.rs:1)
+- [fn is_empty_disk(disk: &Disk)](../src/idempotency/mod.rs:1)
+- [fn which_tool(name: &str)](../src/util/mod.rs:1)
+- [fn run_cmd(args: &[&str])](../src/util/mod.rs:1)
+- [fn run_cmd_capture(args: &[&str])](../src/util/mod.rs:1)
+- [fn udev_settle(timeout_ms: u64)](../src/util/mod.rs:1)
\ No newline at end of file
diff --git a/docs/API.md b/docs/API.md
index 5ef1665..97efc48 100644
--- a/docs/API.md
+++ b/docs/API.md
@@ -8,40 +8,40 @@ Conventions
 - External tooling calls are mediated via utility wrappers.
 
 Module index
-- [src/main.rs](src/main.rs)
-- [src/lib.rs](src/lib.rs)
-- [src/errors.rs](src/errors.rs)
-- [src/cli/args.rs](src/cli/args.rs)
-- [src/logging/mod.rs](src/logging/mod.rs)
-- [src/types.rs](src/types.rs)
-- [src/config/loader.rs](src/config/loader.rs)
-- [src/device/discovery.rs](src/device/discovery.rs)
-- [src/partition/plan.rs](src/partition/plan.rs)
-- [src/fs/plan.rs](src/fs/plan.rs)
-- [src/mount/ops.rs](src/mount/ops.rs)
-- [src/report/state.rs](src/report/state.rs)
-- [src/orchestrator/run.rs](src/orchestrator/run.rs)
-- [src/idempotency/mod.rs](src/idempotency/mod.rs)
-- [src/util/mod.rs](src/util/mod.rs)
+- [src/main.rs](../src/main.rs)
+- [src/lib.rs](../src/lib.rs)
+- [src/errors.rs](../src/errors.rs)
+- [src/cli/args.rs](../src/cli/args.rs)
+- [src/logging/mod.rs](../src/logging/mod.rs)
+- [src/types.rs](../src/types.rs)
+- [src/config/loader.rs](../src/config/loader.rs)
+- [src/device/discovery.rs](../src/device/discovery.rs)
+- [src/partition/plan.rs](../src/partition/plan.rs)
+- [src/fs/plan.rs](../src/fs/plan.rs)
+- [src/mount/ops.rs](../src/mount/ops.rs)
+- [src/report/state.rs](../src/report/state.rs)
+- [src/orchestrator/run.rs](../src/orchestrator/run.rs)
+- [src/idempotency/mod.rs](../src/idempotency/mod.rs)
+- [src/util/mod.rs](../src/util/mod.rs)
 
 Common errors and result
-- [enum Error](src/errors.rs:1)
+- [enum Error](../src/errors.rs:1)
   - Top-level error type covering parse/validation errors, device discovery errors, partitioning failures, filesystem mkfs errors, mount errors, report write errors, and external tool invocation failures with stderr capture.
-- [type Result<T> = std::result::Result<T, Error>](src/errors.rs:1)
+- [type Result<T> = std::result::Result<T, Error>](../src/errors.rs:1)
   - Shared result alias across modules.
 
 Crate root
-- [src/lib.rs](src/lib.rs)
+- [src/lib.rs](../src/lib.rs)
   - Exposes crate version constants, the prelude, and re-exports common types for consumers of the library (tests/integration). No heavy logic.
 
 Entrypoint
-- [fn main()](src/main.rs:1)
+- [fn main()](../src/main.rs:1)
   - Initializes logging based on CLI defaults, parses CLI flags and kernel cmdline, loads and validates configuration, and invokes the orchestrator run sequence. Avoids stdout; logs via tracing only.
 
 Orchestrator
-- [struct Context](src/orchestrator/run.rs:1)
+- [struct Context](../src/orchestrator/run.rs:1)
   - Aggregates resolved configuration, logging options, and environment flags suited for initramfs execution.
-- [fn run(ctx: &Context) -> Result<()>](src/orchestrator/run.rs:1)
+- [fn run(ctx: &Context) -> Result<()>](../src/orchestrator/run.rs:1)
   - High-level one-shot flow:
     - Idempotency detection
     - Device discovery
@@ -52,131 +52,141 @@ Orchestrator
   - Aborts the entire run on any validation or execution failure. Returns Ok on successful no-op if already provisioned.
 
 CLI
-- [struct Cli](src/cli/args.rs:1)
+- [struct Cli](../src/cli/args.rs:1)
   - Mirrors kernel cmdline semantics with flags:
     - --config PATH
     - --log-level LEVEL
     - --log-to-file
     - --fstab
+    - --show
+    - --report PATH
+    - --apply
     - --force (present, returns unimplemented error)
-- [fn from_args() -> Cli](src/cli/args.rs:1)
+- [fn from_args() -> Cli](../src/cli/args.rs:1)
   - Parses argv without side effects; suitable for initramfs.
 
 Logging
-- [struct LogOptions](src/logging/mod.rs:1)
+- [struct LogOptions](../src/logging/mod.rs:1)
   - Holds level and optional file target (/run/zosstorage/zosstorage.log).
-- [fn init_logging(opts: &LogOptions) -> Result<()>](src/logging/mod.rs:1)
+- [fn init_logging(opts: &LogOptions) -> Result<()>](../src/logging/mod.rs:1)
   - Configures tracing-subscriber for stderr by default and optional file layer when enabled. Must be idempotent.
 
 Configuration types
-- [struct Config](src/types.rs:1)
+- [struct Config](../src/types.rs:1)
   - The validated configuration used by the orchestrator, containing logging, device selection rules, topology, partitioning, filesystem options, mount scheme, and report path.
-- [enum Topology](src/types.rs:1)
-  - Values: btrfs_single, bcachefs_single, dual_independent, bcachefs_2copy, ssd_hdd_bcachefs, btrfs_raid1 (opt-in).
-- [struct DeviceSelection](src/types.rs:1)
+- [enum Topology](../src/types.rs:1)
+  - Values: btrfs_single, bcachefs_single, dual_independent, bcachefs2_copy, ssd_hdd_bcachefs, btrfs_raid1 (opt-in).
+- [struct DeviceSelection](../src/types.rs:1)
   - Include and exclude regex patterns, minimum size, removable policy.
-- [struct Partitioning](src/types.rs:1)
+- [struct Partitioning](../src/types.rs:1)
   - Alignment, emptiness requirement, bios_boot, esp, data, cache GPT names and sizes where applicable.
-- [struct BtrfsOptions](src/types.rs:1)
+- [struct BtrfsOptions](../src/types.rs:1)
   - Compression string and raid profile (none or raid1).
-- [struct BcachefsOptions](src/types.rs:1)
+- [struct BcachefsOptions](../src/types.rs:1)
   - Cache mode (promote or writeback), compression, checksum.
-- [struct VfatOptions](src/types.rs:1)
+- [struct VfatOptions](../src/types.rs:1)
   - Reserved for ESP mkfs options; includes label ZOSBOOT.
-- [struct FsOptions](src/types.rs:1)
+- [struct FsOptions](../src/types.rs:1)
   - Aggregates BtrfsOptions, BcachefsOptions, VfatOptions and shared defaults such as ZOSDATA label.
-- [enum MountSchemeKind](src/types.rs:1)
+- [enum MountSchemeKind](../src/types.rs:1)
   - Values: per_uuid, custom (future).
-- [struct MountScheme](src/types.rs:1)
+- [struct MountScheme](../src/types.rs:1)
   - Base directory (/var/cache), scheme kind, fstab enabled flag.
-- [struct ReportOptions](src/types.rs:1)
+- [struct ReportOptions](../src/types.rs:1)
   - Output path (/run/zosstorage/state.json).
 
 Configuration IO
-- [fn load_and_merge(cli: &Cli) -> Result<Config>](src/config/loader.rs:1)
+- [fn load_and_merge(cli: &Cli) -> Result<Config>](../src/config/loader.rs:1)
   - Loads built-in defaults, optionally merges on-disk config, overlays CLI flags, and finally overlays kernel cmdline via zosstorage.config=. Validates the YAML against types and constraints.
-- [fn validate(cfg: &Config) -> Result<()>](src/config/loader.rs:1)
+- [fn validate(cfg: &Config) -> Result<()>](../src/config/loader.rs:1)
   - Ensures structural and semantic validity (e.g., disk selection rules not empty, sizes non-zero, supported topology combinations).
 
 Device discovery
-- [struct Disk](src/device/discovery.rs:1)
+- [struct Disk](../src/device/discovery.rs:1)
   - Represents an eligible block device with path, size, rotational flag, and identifiers (serial, model if available).
-- [struct DeviceFilter](src/device/discovery.rs:1)
+- [struct DeviceFilter](../src/device/discovery.rs:1)
   - Derived from DeviceSelection; compiled regexes and size thresholds for efficient filtering.
-- [trait DeviceProvider](src/device/discovery.rs:1)
+- [trait DeviceProvider](../src/device/discovery.rs:1)
   - Abstraction for listing /dev and probing properties, enabling test doubles.
-- [fn discover(filter: &DeviceFilter) -> Result<Vec<Disk>>](src/device/discovery.rs:1)
+- [fn discover(filter: &DeviceFilter) -> Result<Vec<Disk>>](../src/device/discovery.rs:1)
   - Returns eligible disks or a well-defined error if none are found.
 
 Partitioning
-- [enum PartRole](src/partition/plan.rs:1)
+- [enum PartRole](../src/partition/plan.rs:1)
   - Roles: BiosBoot, Esp, Data, Cache.
-- [struct PartitionSpec](src/partition/plan.rs:1)
+- [struct PartitionSpec](../src/partition/plan.rs:1)
   - Declarative spec for a single partition: role, optional size_mib, gpt_name (zosboot, zosdata, zoscache), and reserved filesystem label when role is Esp (ZOSBOOT).
-- [struct DiskPlan](src/partition/plan.rs:1)
+- [struct DiskPlan](../src/partition/plan.rs:1)
   - The planned set of PartitionSpec instances for a single Disk in the chosen topology.
-- [struct PartitionPlan](src/partition/plan.rs:1)
+- [struct PartitionPlan](../src/partition/plan.rs:1)
   - Combined plan across all target disks, including alignment rules and safety checks.
-- [struct PartitionResult](src/partition/plan.rs:1)
+- [struct PartitionResult](../src/partition/plan.rs:1)
   - Result of applying a DiskPlan: device path of each created partition, role, partition GUID, and gpt_name.
-- [fn plan_partitions(disks: &[Disk], cfg: &Config) -> Result<PartitionPlan>](src/partition/plan.rs:1)
+- [fn plan_partitions(disks: &[Disk], cfg: &Config) -> Result<PartitionPlan>](../src/partition/plan.rs:1)
   - Produces a GPT-only plan with 1 MiB alignment, bios boot first (1 MiB), ESP 512 MiB, data remainder, and zoscache on SSD for ssd_hdd_bcachefs.
-- [fn apply_partitions(plan: &PartitionPlan) -> Result<Vec<PartitionResult>>](src/partition/plan.rs:1)
+- [fn apply_partitions(plan: &PartitionPlan) -> Result<Vec<PartitionResult>>](../src/partition/plan.rs:1)
   - Executes the plan via sgdisk and related utilities. Aborts if target disks are not empty or if signatures are detected.
 
 Filesystems
-- [enum FsKind](src/fs/plan.rs:1)
+- [enum FsKind](../src/fs/plan.rs:1)
   - Values: Vfat, Btrfs, Bcachefs.
-- [struct FsSpec](src/fs/plan.rs:1)
+- [struct FsSpec](../src/fs/plan.rs:1)
   - Maps PartitionResult to desired filesystem kind and label (ZOSBOOT for ESP; ZOSDATA for all data filesystems including bcachefs).
-- [struct FsPlan](src/fs/plan.rs:1)
+- [struct FsPlan](../src/fs/plan.rs:1)
   - Plan of mkfs operations across all partitions and devices given the topology.
-- [struct FsResult](src/fs/plan.rs:1)
+- [struct FsResult](../src/fs/plan.rs:1)
   - Output of mkfs: device path(s), fs uuid, label, and kind.
-- [fn plan_filesystems(disks: &[Disk], parts: &[PartitionResult], cfg: &Config) -> Result<FsPlan>](src/fs/plan.rs:1)
+- [fn plan_filesystems(disks: &[Disk], parts: &[PartitionResult], cfg: &Config) -> Result<FsPlan>](../src/fs/plan.rs:1)
   - Determines which partitions receive vfat, btrfs, or bcachefs, and aggregates tuning options.
-- [fn make_filesystems(plan: &FsPlan) -> Result<Vec<FsResult>>](src/fs/plan.rs:1)
+- [fn make_filesystems(plan: &FsPlan, cfg: &Config) -> Result<Vec<FsResult>>](../src/fs/plan.rs:1)
   - Invokes mkfs.vfat, mkfs.btrfs, mkfs.bcachefs accordingly via utility wrappers and returns filesystem identities.
 
 Mounting
-- [struct MountPlan](src/mount/ops.rs:1)
-  - Derived from FsResult entries: creates target directories under /var/cache/<UUID> and the mounts required for the current boot.
-- [struct MountResult](src/mount/ops.rs:1)
+- [struct MountPlan](../src/mount/ops.rs:1)
+  - Derived from FsResult entries. Plans:
+    - Root mounts for all data filesystems under `/var/mounts/{UUID}` (runtime only).
+      - btrfs root options: `rw,noatime,subvolid=5`
+      - bcachefs root options: `rw,noatime`
+    - Final subvolume/subdir mounts (from the primary data filesystem) to:
+      - `/var/cache/system`, `/var/cache/etc`, `/var/cache/modules`, `/var/cache/vm-meta`
+- [struct MountResult](../src/mount/ops.rs:1)
   - Actual mount operations performed (source, target, fstype, options).
-- [fn plan_mounts(fs_results: &[FsResult], cfg: &Config) -> Result<MountPlan>](src/mount/ops.rs:1)
-  - Translates filesystem identities to mount targets and options.
-- [fn apply_mounts(plan: &MountPlan) -> Result<Vec<MountResult>>](src/mount/ops.rs:1)
-  - Performs mounts using syscalls (nix crate) with minimal dependencies. Ensures directories exist.
-- [fn maybe_write_fstab(mounts: &[MountResult], cfg: &Config) -> Result<()>](src/mount/ops.rs:1)
-  - When enabled, generates /etc/fstab entries in deterministic order. Disabled by default.
+- [fn plan_mounts(fs_results: &[FsResult], cfg: &Config) -> Result<MountPlan>](../src/mount/ops.rs:1)
+  - Translates filesystem identities to mount targets and options, including `subvol=` for btrfs and `X-mount.subdir=` for bcachefs.
+- [fn apply_mounts(plan: &MountPlan) -> Result<Vec<MountResult>>](../src/mount/ops.rs:1)
+  - Performs mounts using syscalls (nix crate). Ensures directories exist and creates subvolumes/subdirs if missing.
+- [fn maybe_write_fstab(mounts: &[MountResult], cfg: &Config) -> Result<()>](../src/mount/ops.rs:1)
+  - When enabled, writes only the four subvolume/subdir mount entries to `/etc/fstab` in deterministic order using `UUID=` sources. Root mounts under `/var/mounts` are excluded.
 
 Reporting
-- [const REPORT_VERSION: &str](src/report/state.rs:1)
+- [const REPORT_VERSION: &str](../src/report/state.rs:1)
   - Version string for the JSON payload schema.
-- [struct StateReport](src/report/state.rs:1)
+- [struct StateReport](../src/report/state.rs:1)
   - Machine-readable state describing discovered disks, created partitions, filesystems, labels, mountpoints, status, and timestamp.
-- [fn build_report(disks: &[Disk], parts: &[PartitionResult], fs: &[FsResult], mounts: &[MountResult], status: &str) -> StateReport](src/report/state.rs:1)
+- [fn build_report(disks: &[Disk], parts: &[PartitionResult], fs: &[FsResult], mounts: &[MountResult], status: &str) -> StateReport](../src/report/state.rs:1)
   - Constructs a StateReport matching REPORT_VERSION.
-- [fn write_report(report: &StateReport) -> Result<()>](src/report/state.rs:1)
+- [fn write_report(report: &StateReport) -> Result<()>](../src/report/state.rs:1)
   - Writes JSON to /run/zosstorage/state.json (configurable).
 
 Idempotency
-- [fn detect_existing_state() -> Result<Option<StateReport>>](src/idempotency/mod.rs:1)
+- [fn detect_existing_state() -> Result<Option<StateReport>>](../src/idempotency/mod.rs:1)
   - Probes for expected GPT names (zosboot, zosdata, zoscache where applicable) and filesystem labels (ZOSBOOT, ZOSDATA). If present and consistent, returns a StateReport; orchestrator exits success without changes.
-- [fn is_empty_disk(disk: &Disk) -> Result<bool>](src/idempotency/mod.rs:1)
+- [fn is_empty_disk(disk: &Disk) -> Result<bool>](../src/idempotency/mod.rs:1)
   - Determines disk emptiness: absence of partitions and known filesystem signatures.
 
 Utilities
-- [struct CmdOutput](src/util/mod.rs:1)
+- [struct CmdOutput](../src/util/mod.rs:1)
   - Captures status, stdout, stderr from external tool invocations.
-- [fn which_tool(name: &str) -> Result<Option<String>>](src/util/mod.rs:1)
+- [fn which_tool(name: &str) -> Result<Option<String>>](../src/util/mod.rs:1)
   - Locates a required system utility in PATH, returning its absolute path if available.
-- [fn run_cmd(args: &[&str]) -> Result<()>](src/util/mod.rs:1)
+- [fn run_cmd(args: &[&str]) -> Result<()>](../src/util/mod.rs:1)
   - Executes a command (args[0] is binary) and returns Ok when exit status is zero; logs stderr on failure.
-- [fn run_cmd_capture(args: &[&str]) -> Result<CmdOutput>](src/util/mod.rs:1)
+- [fn run_cmd_capture(args: &[&str]) -> Result<CmdOutput>](../src/util/mod.rs:1)
   - Executes a command and returns captured output for parsing (e.g., blkid).
-- [fn udev_settle(timeout_ms: u64) -> Result<()>](src/util/mod.rs:1)
+- [fn udev_settle(timeout_ms: u64) -> Result<()>](../src/util/mod.rs:1)
   - Calls udevadm settle with a timeout when available; otherwise no-ops with a warning.
+- [fn is_efi_boot() -> bool](../src/util/mod.rs:1)
+  - Detects UEFI environment by checking `/sys/firmware/efi`; used to suppress BIOS boot partition creation on UEFI systems.
 
 Behavioral notes and contracts
 - Safety and idempotency:
@@ -188,10 +198,13 @@ Behavioral notes and contracts
   - Data filesystems use label ZOSDATA regardless of backend kind.
   - Cache partitions in bcachefs topology use GPT name zoscache.
 - Topology-specific behavior:
-  - single: one data filesystem (btrfs) on the sole disk.
-  - dual_independent: two separate btrfs filesystems, one per disk.
+  - btrfs_single: one data filesystem (btrfs) on the sole disk.
+  - bcachefs_single: one data filesystem (bcachefs) on the sole disk.
+  - dual_independent: independent btrfs filesystems on each eligible disk (one or more).
+  - bcachefs2_copy: multi-device bcachefs across two or more data partitions with `--replicas=2` (data and metadata).
   - ssd_hdd_bcachefs: bcachefs spanning SSD (cache/promote) and HDD (backing), labeled ZOSDATA.
   - btrfs_raid1: only when explicitly requested; otherwise default to independent btrfs.
+- UEFI vs BIOS: when running under UEFI (`/sys/firmware/efi` present), the BIOS boot partition is suppressed.
 
 Module dependency overview
 
diff --git a/docs/ARCHITECTURE.md b/docs/ARCHITECTURE.md
index e14af8e..daf93c1 100644
--- a/docs/ARCHITECTURE.md
+++ b/docs/ARCHITECTURE.md
@@ -30,116 +30,122 @@ Top level
   - [tests/integration_ssd_hdd.rs](tests/integration_ssd_hdd.rs)
 
 Crate sources
-- [src/main.rs](src/main.rs)
-- [src/lib.rs](src/lib.rs)
-- [src/errors.rs](src/errors.rs)
-- [src/cli/args.rs](src/cli/args.rs)
-- [src/logging/mod.rs](src/logging/mod.rs)
-- [src/config/loader.rs](src/config/loader.rs)
-- [src/types.rs](src/types.rs)
-- [src/device/discovery.rs](src/device/discovery.rs)
-- [src/partition/plan.rs](src/partition/plan.rs)
-- [src/fs/plan.rs](src/fs/plan.rs)
-- [src/mount/ops.rs](src/mount/ops.rs)
-- [src/report/state.rs](src/report/state.rs)
-- [src/orchestrator/run.rs](src/orchestrator/run.rs)
-- [src/idempotency/mod.rs](src/idempotency/mod.rs)
-- [src/util/mod.rs](src/util/mod.rs)
+- [src/main.rs](../src/main.rs)
+- [src/lib.rs](../src/lib.rs)
+- [src/errors.rs](../src/errors.rs)
+- [src/cli/args.rs](../src/cli/args.rs)
+- [src/logging/mod.rs](../src/logging/mod.rs)
+- [src/config/loader.rs](../src/config/loader.rs)
+- [src/types.rs](../src/types.rs)
+- [src/device/discovery.rs](../src/device/discovery.rs)
+- [src/partition/plan.rs](../src/partition/plan.rs)
+- [src/fs/plan.rs](../src/fs/plan.rs)
+- [src/mount/ops.rs](../src/mount/ops.rs)
+- [src/report/state.rs](../src/report/state.rs)
+- [src/orchestrator/run.rs](../src/orchestrator/run.rs)
+- [src/idempotency/mod.rs](../src/idempotency/mod.rs)
+- [src/util/mod.rs](../src/util/mod.rs)
 
 Module responsibilities
-- [src/main.rs](src/main.rs)
+- [src/main.rs](../src/main.rs)
   - Entrypoint. Parse CLI, initialize logging, load and merge configuration per precedence, call orchestrator. No stdout spam.
-- [src/lib.rs](src/lib.rs)
+- [src/lib.rs](../src/lib.rs)
   - Crate exports, prelude, version constants, Result alias.
-- [src/errors.rs](src/errors.rs)
+- [src/errors.rs](../src/errors.rs)
   - Common error enum and Result alias via thiserror.
-- [src/cli/args.rs](src/cli/args.rs)
+- [src/cli/args.rs](../src/cli/args.rs)
   - CLI definition mirroring kernel cmdline semantics; provide non-interactive interface. Stub --force returns unimplemented.
-- [src/logging/mod.rs](src/logging/mod.rs)
+- [src/logging/mod.rs](../src/logging/mod.rs)
   - Initialize tracing; levels error, warn, info, debug; default to stderr; optional file target.
-- [src/config/loader.rs](src/config/loader.rs) and [src/types.rs](src/types.rs)
+- [src/config/loader.rs](../src/config/loader.rs) and [src/types.rs](../src/types.rs)
   - YAML schema types, validation, loading, and merging with CLI and kernel cmdline.
-- [src/device/discovery.rs](src/device/discovery.rs)
+- [src/device/discovery.rs](../src/device/discovery.rs)
   - Device discovery under /dev with filters and allowlist; probe emptiness safely.
-- [src/partition/plan.rs](src/partition/plan.rs)
+- [src/partition/plan.rs](../src/partition/plan.rs)
   - GPT-only planning and application; 1 MiB alignment; create bios boot, ESP, data and cache partitions with strict safety checks.
-- [src/fs/plan.rs](src/fs/plan.rs)
+- [src/fs/plan.rs](../src/fs/plan.rs)
   - Filesystem provisioning: vfat for ESP, btrfs for ZOSDATA, bcachefs for SSD+HDD mode; all data filesystems labeled ZOSDATA.
-- [src/mount/ops.rs](src/mount/ops.rs)
-  - Mount per-UUID under /var/cache/<UUID>. Optional fstab writing, disabled by default.
-- [src/report/state.rs](src/report/state.rs)
+- [src/mount/ops.rs](../src/mount/ops.rs)
+  - Mount scheme:
+    - Root-mount all data filesystems under `/var/mounts/{UUID}` (runtime only)
+      - btrfs root: `rw,noatime,subvolid=5`
+      - bcachefs root: `rw,noatime`
+    - Create or ensure subvolumes on the primary data filesystem: `system`, `etc`, `modules`, `vm-meta`
+    - Mount final subvolume/subdir targets at `/var/cache/{system,etc,modules,vm-meta}`
+    - Optional fstab writing: only the four final targets, deterministic order, `UUID=` sources; disabled by default
+- [src/report/state.rs](../src/report/state.rs)
   - Build and write JSON state report with version field.
-- [src/orchestrator/run.rs](src/orchestrator/run.rs)
+- [src/orchestrator/run.rs](../src/orchestrator/run.rs)
   - One-shot flow orchestration with abort-on-any-validation-error policy.
-- [src/idempotency/mod.rs](src/idempotency/mod.rs)
+- [src/idempotency/mod.rs](../src/idempotency/mod.rs)
   - Detect prior provisioning via GPT names and labels; return success-without-changes.
-- [src/util/mod.rs](src/util/mod.rs)
+- [src/util/mod.rs](../src/util/mod.rs)
   - Shell-out, udev settle, and helpers.
 
 Public API surface (signatures; implementation to follow after approval)
 Entrypoint and orchestrator
-- [fn main()](src/main.rs:1)
-- [struct Context](src/orchestrator/run.rs:1)
-- [fn run(ctx: &Context) -> Result<()>](src/orchestrator/run.rs:1)
+- [fn main()](../src/main.rs:1)
+- [struct Context](../src/orchestrator/run.rs:1)
+- [fn run(ctx: &Context) -> Result<()>](../src/orchestrator/run.rs:1)
 
 CLI
-- [struct Cli](src/cli/args.rs:1)
-- [fn from_args() -> Cli](src/cli/args.rs:1)
+- [struct Cli](../src/cli/args.rs:1)
+- [fn from_args() -> Cli](../src/cli/args.rs:1)
 
 Logging
-- [struct LogOptions](src/logging/mod.rs:1)
-- [fn init_logging(opts: &LogOptions) -> Result<()>](src/logging/mod.rs:1)
+- [struct LogOptions](../src/logging/mod.rs:1)
+- [fn init_logging(opts: &LogOptions) -> Result<()>](../src/logging/mod.rs:1)
 
 Config
-- [struct Config](src/types.rs:1)
-- [enum Topology](src/types.rs:1)
-- [struct DeviceSelection](src/types.rs:1)
-- [struct FsOptions](src/types.rs:1)
-- [struct MountScheme](src/types.rs:1)
-- [fn load_and_merge(cli: &Cli) -> Result<Config>](src/config/loader.rs:1)
-- [fn validate(cfg: &Config) -> Result<()>](src/config/loader.rs:1)
+- [struct Config](../src/types.rs:1)
+- [enum Topology](../src/types.rs:1)
+- [struct DeviceSelection](../src/types.rs:1)
+- [struct FsOptions](../src/types.rs:1)
+- [struct MountScheme](../src/types.rs:1)
+- [fn load_and_merge(cli: &Cli) -> Result<Config>](../src/config/loader.rs:1)
+- [fn validate(cfg: &Config) -> Result<()>](../src/config/loader.rs:1)
 
 Device discovery
-- [struct Disk](src/device/discovery.rs:1)
-- [struct DeviceFilter](src/device/discovery.rs:1)
-- [trait DeviceProvider](src/device/discovery.rs:1)
-- [fn discover(filter: &DeviceFilter) -> Result<Vec<Disk>>](src/device/discovery.rs:1)
+- [struct Disk](../src/device/discovery.rs:1)
+- [struct DeviceFilter](../src/device/discovery.rs:1)
+- [trait DeviceProvider](../src/device/discovery.rs:1)
+- [fn discover(filter: &DeviceFilter) -> Result<Vec<Disk>>](../src/device/discovery.rs:1)
 
 Partitioning
-- [struct PartitionSpec](src/partition/plan.rs:1)
-- [struct PartitionPlan](src/partition/plan.rs:1)
-- [struct PartitionResult](src/partition/plan.rs:1)
-- [fn plan_partitions(disks: &[Disk], cfg: &Config) -> Result<PartitionPlan>](src/partition/plan.rs:1)
-- [fn apply_partitions(plan: &PartitionPlan) -> Result<Vec<PartitionResult>>](src/partition/plan.rs:1)
+- [struct PartitionSpec](../src/partition/plan.rs:1)
+- [struct PartitionPlan](../src/partition/plan.rs:1)
+- [struct PartitionResult](../src/partition/plan.rs:1)
+- [fn plan_partitions(disks: &[Disk], cfg: &Config) -> Result<PartitionPlan>](../src/partition/plan.rs:1)
+- [fn apply_partitions(plan: &PartitionPlan) -> Result<Vec<PartitionResult>>](../src/partition/plan.rs:1)
 
 Filesystems
-- [enum FsKind](src/fs/plan.rs:1)
-- [struct FsSpec](src/fs/plan.rs:1)
-- [struct FsPlan](src/fs/plan.rs:1)
-- [struct FsResult](src/fs/plan.rs:1)
-- [fn plan_filesystems(disks: &[Disk], parts: &[PartitionResult], cfg: &Config) -> Result<FsPlan>](src/fs/plan.rs:1)
-- [fn make_filesystems(plan: &FsPlan) -> Result<Vec<FsResult>>](src/fs/plan.rs:1)
+- [enum FsKind](../src/fs/plan.rs:1)
+- [struct FsSpec](../src/fs/plan.rs:1)
+- [struct FsPlan](../src/fs/plan.rs:1)
+- [struct FsResult](../src/fs/plan.rs:1)
+- [fn plan_filesystems(disks: &[Disk], parts: &[PartitionResult], cfg: &Config) -> Result<FsPlan>](../src/fs/plan.rs:1)
+- [fn make_filesystems(plan: &FsPlan) -> Result<Vec<FsResult>>](../src/fs/plan.rs:1)
 
 Mounting
-- [struct MountPlan](src/mount/ops.rs:1)
-- [struct MountResult](src/mount/ops.rs:1)
-- [fn plan_mounts(fs_results: &[FsResult], cfg: &Config) -> Result<MountPlan>](src/mount/ops.rs:1)
-- [fn apply_mounts(plan: &MountPlan) -> Result<Vec<MountResult>>](src/mount/ops.rs:1)
-- [fn maybe_write_fstab(mounts: &[MountResult], cfg: &Config) -> Result<()>](src/mount/ops.rs:1)
+- [struct MountPlan](../src/mount/ops.rs:1)
+- [struct MountResult](../src/mount/ops.rs:1)
+- [fn plan_mounts(fs_results: &[FsResult], cfg: &Config) -> Result<MountPlan>](../src/mount/ops.rs:1)
+- [fn apply_mounts(plan: &MountPlan) -> Result<Vec<MountResult>>](../src/mount/ops.rs:1)
+- [fn maybe_write_fstab(mounts: &[MountResult], cfg: &Config) -> Result<()>](../src/mount/ops.rs:1)
 
 Reporting
-- [const REPORT_VERSION: &str](src/report/state.rs:1)
-- [struct StateReport](src/report/state.rs:1)
-- [fn build_report(...) -> StateReport](src/report/state.rs:1)
-- [fn write_report(report: &StateReport) -> Result<()>](src/report/state.rs:1)
+- [const REPORT_VERSION: &str](../src/report/state.rs:1)
+- [struct StateReport](../src/report/state.rs:1)
+- [fn build_report(...) -> StateReport](../src/report/state.rs:1)
+- [fn write_report(report: &StateReport) -> Result<()>](../src/report/state.rs:1)
 
 Idempotency
-- [fn detect_existing_state() -> Result<Option<StateReport>>](src/idempotency/mod.rs:1)
-- [fn is_empty_disk(disk: &Disk) -> Result<bool>](src/idempotency/mod.rs:1)
+- [fn detect_existing_state() -> Result<Option<StateReport>>](../src/idempotency/mod.rs:1)
+- [fn is_empty_disk(disk: &Disk) -> Result<bool>](../src/idempotency/mod.rs:1)
 
 Errors and Result
-- [enum Error](src/errors.rs:1)
-- [type Result<T> = std::result::Result<T, Error>](src/errors.rs:1)
+- [enum Error](../src/errors.rs:1)
+- [type Result<T> = std::result::Result<T, Error>](../src/errors.rs:1)
 
 Execution flow
 
@@ -190,8 +196,15 @@ Filesystem provisioning defaults
 - Filesystem tuning options configurable with sensible defaults and extension points
 
 Mount scheme and fstab policy
-- Mount under /var/cache/<UUID> using filesystem UUID to create stable subdirectories
-- Optional /etc/fstab generation disabled by default; when enabled, produce deterministic order with documentation
+- Runtime root mounts:
+  - Each data filesystem is root-mounted at `/var/mounts/{UUID}` (runtime only)
+  - btrfs: `rw,noatime,subvolid=5`; bcachefs: `rw,noatime`
+- Final targets (from primary data filesystem only):
+  - `/var/cache/system`, `/var/cache/etc`, `/var/cache/modules`, `/var/cache/vm-meta`
+  - btrfs subvolume option: `-o subvol={name},noatime`
+  - bcachefs subdir option: `-o X-mount.subdir={name},noatime`
+- /etc/fstab generation:
+  - Disabled by default. When enabled, write only the four final targets with `UUID=` sources in deterministic order. Root mounts under `/var/mounts` are excluded.
 
 Idempotency detection
 - Consider the system provisioned when expected GPT names and filesystem labels are present and consistent
diff --git a/docs/DEV_WORKFLOW.md b/docs/DEV_WORKFLOW.md
index 00893cb..4fc5459 100644
--- a/docs/DEV_WORKFLOW.md
+++ b/docs/DEV_WORKFLOW.md
@@ -8,18 +8,18 @@ Goal
 Core Principles
 1) Contract-first per module
    - API signatures and responsibilities are documented in [docs/API-SKELETONS.md](docs/API-SKELETONS.md) and mirrored by crate modules:
-     - [src/types.rs](src/types.rs)
-     - [fn load_and_merge()](src/config/loader.rs:1), [fn validate()](src/config/loader.rs:1)
-     - [fn from_args()](src/cli/args.rs:1)
-     - [struct LogOptions](src/logging/mod.rs:1), [fn init_logging()](src/logging/mod.rs:1)
-     - [fn discover()](src/device/discovery.rs:1)
-     - [fn plan_partitions()](src/partition/plan.rs:1), [fn apply_partitions()](src/partition/plan.rs:1)
-     - [fn plan_filesystems()](src/fs/plan.rs:1), [fn make_filesystems()](src/fs/plan.rs:1)
-     - [fn plan_mounts()](src/mount/ops.rs:1), [fn apply_mounts()](src/mount/ops.rs:1), [fn maybe_write_fstab()](src/mount/ops.rs:1)
-     - [const REPORT_VERSION](src/report/state.rs:1), [fn build_report()](src/report/state.rs:1), [fn write_report()](src/report/state.rs:1)
-     - [struct Context](src/orchestrator/run.rs:1), [fn run()](src/orchestrator/run.rs:1)
-     - [fn detect_existing_state()](src/idempotency/mod.rs:1), [fn is_empty_disk()](src/idempotency/mod.rs:1)
-     - [struct CmdOutput](src/util/mod.rs:1), [fn which_tool()](src/util/mod.rs:1), [fn run_cmd()](src/util/mod.rs:1), [fn run_cmd_capture()](src/util/mod.rs:1), [fn udev_settle()](src/util/mod.rs:1)
+     - [src/types.rs](../src/types.rs)
+     - [fn load_and_merge()](../src/config/loader.rs:1), [fn validate()](../src/config/loader.rs:1)
+     - [fn from_args()](../src/cli/args.rs:1)
+     - [struct LogOptions](../src/logging/mod.rs:1), [fn init_logging()](../src/logging/mod.rs:1)
+     - [fn discover()](../src/device/discovery.rs:1)
+     - [fn plan_partitions()](../src/partition/plan.rs:1), [fn apply_partitions()](../src/partition/plan.rs:1)
+     - [fn plan_filesystems()](../src/fs/plan.rs:1), [fn make_filesystems()](../src/fs/plan.rs:1)
+     - [fn plan_mounts()](../src/mount/ops.rs:1), [fn apply_mounts()](../src/mount/ops.rs:1), [fn maybe_write_fstab()](../src/mount/ops.rs:1)
+     - [const REPORT_VERSION](../src/report/state.rs:1), [fn build_report()](../src/report/state.rs:1), [fn write_report()](../src/report/state.rs:1)
+     - [struct Context](../src/orchestrator/run.rs:1), [fn run()](../src/orchestrator/run.rs:1)
+     - [fn detect_existing_state()](../src/idempotency/mod.rs:1), [fn is_empty_disk()](../src/idempotency/mod.rs:1)
+     - [struct CmdOutput](../src/util/mod.rs:1), [fn which_tool()](../src/util/mod.rs:1), [fn run_cmd()](../src/util/mod.rs:1), [fn run_cmd_capture()](../src/util/mod.rs:1), [fn udev_settle()](../src/util/mod.rs:1)
 
 2) Grep-able region markers in code
    - Every module contains the following optional annotated regions:
@@ -55,22 +55,22 @@ Core Principles
 6) Module ownership and boundaries
    - Add a “Module Responsibilities” section in each module’s header doc comment summarizing scope and non-goals.
    - Example references:
-     - [src/device/discovery.rs](src/device/discovery.rs)
-     - [src/partition/plan.rs](src/partition/plan.rs)
-     - [src/fs/plan.rs](src/fs/plan.rs)
-     - [src/mount/ops.rs](src/mount/ops.rs)
-     - [src/report/state.rs](src/report/state.rs)
+     - [src/device/discovery.rs](../src/device/discovery.rs)
+     - [src/partition/plan.rs](../src/partition/plan.rs)
+     - [src/fs/plan.rs](../src/fs/plan.rs)
+     - [src/mount/ops.rs](../src/mount/ops.rs)
+     - [src/report/state.rs](../src/report/state.rs)
 
 7) Invariants and safety notes
    - For code that must uphold safety or idempotency invariants, annotate with:
      // SAFETY: explanation
      // IDEMPOTENCY: explanation
    - Example locations:
-     - [fn apply_partitions()](src/partition/plan.rs:1) must enforce empty-disks rule when configured.
-     - [fn make_filesystems()](src/fs/plan.rs:1) must not run if partitioning failed.
+     - [fn apply_partitions()](../src/partition/plan.rs:1) must enforce empty-disks rule when configured.
+     - [fn make_filesystems()](../src/fs/plan.rs:1) must not run if partitioning failed.
 
 8) Error mapping consistency
-   - Centralize conversions to [enum Error](src/errors.rs:1). When calling external tools, wrap failures into Error::Tool with stderr captured.
+   - Centralize conversions to [enum Error](../src/errors.rs:1). When calling external tools, wrap failures into Error::Tool with stderr captured.
    - Annotate mapping areas with:
      // ERROR: mapping external failure to Error::Tool
 
@@ -111,7 +111,7 @@ Checklist for adding a new feature
 - Add examples if config or output formats change
   - Update [config/zosstorage.example.yaml](config/zosstorage.example.yaml) or add a new example file
 - Keep error mapping and logging consistent:
-  - Ensure any external tool calls map errors to [enum Error](src/errors.rs:1)
+  - Ensure any external tool calls map errors to [enum Error](../src/errors.rs:1)
 - Run cargo build and update any broken references
 
 Optional automation (future)
diff --git a/docs/SCHEMA.md b/docs/SCHEMA.md
index 0a7fc49..94bcff1 100644
--- a/docs/SCHEMA.md
+++ b/docs/SCHEMA.md
@@ -43,7 +43,7 @@ device_selection:
   allow_removable: false     # future option; default false
   min_size_gib: 10           # ignore devices smaller than this (default 10)
 topology:                    # desired overall layout; see values below
-  mode: single               # single | dual_independent | ssd_hdd_bcachefs | btrfs_raid1 (optional)
+  mode: btrfs_single         # btrfs_single | bcachefs_single | dual_independent | bcachefs2_copy | ssd_hdd_bcachefs | btrfs_raid1
 partitioning:
   alignment_mib: 1           # GPT alignment in MiB
   require_empty_disks: true  # abort if any partition or FS signatures exist
@@ -83,8 +83,8 @@ report:
 Topology modes
 - btrfs_single: One eligible disk. Create BIOS boot (if enabled), ESP 512 MiB, remainder as data. Create a btrfs filesystem labeled ZOSDATA on the data partition.
 - bcachefs_single: One eligible disk. Create BIOS boot (if enabled), ESP 512 MiB, remainder as data. Create a bcachefs filesystem labeled ZOSDATA on the data partition.
-- dual_independent: Two eligible disks. On each disk, create BIOS boot (if enabled) + ESP + data. Create an independent btrfs filesystem labeled ZOSDATA on each data partition. No RAID by default.
-- bcachefs_2copy: Two eligible disks. Create data partitions on both, then create a single multi-device bcachefs labeled ZOSDATA spanning the data partitions (two-copies semantics to be tuned via mkfs options in a follow-up).
+- dual_independent: One or more eligible disks. On each disk, create BIOS boot (if enabled) + ESP + data. Create an independent btrfs filesystem labeled ZOSDATA on each data partition. No RAID by default.
+- bcachefs2_copy: Two or more eligible disks (minimum 2). Create data partitions and then a single multi-device bcachefs labeled ZOSDATA spanning those data partitions. The mkfs step uses `--replicas=2` (data and metadata).
 - ssd_hdd_bcachefs: One SSD/NVMe and one HDD. Create BIOS boot (if enabled) + ESP on both as required. Create cache (on SSD) and data/backing (on HDD) partitions named zoscache and zosdata respectively. Create a bcachefs labeled ZOSDATA across SSD(HDD) per policy (SSD cache/promote; HDD backing).
 - btrfs_raid1: Optional mode if explicitly requested. Create mirrored btrfs across two disks for the data role with raid1 profile. Not enabled by default.
 
@@ -119,11 +119,15 @@ Filesystem section
 - vfat: label ZOSBOOT used for ESP.
 
 Mount section
-- base_dir: default /var/cache.
-- scheme:
-  - per_uuid: mount data filesystems at /var/cache/<FS-UUID>
-  - custom: reserved for future mapping-by-config, not yet implemented.
-- fstab.enabled: default false. When true, zosstorage will generate fstab entries in deterministic order.
+- Runtime root mounts (all data filesystems):
+  - Each data filesystem is root-mounted at `/var/mounts/{UUID}`
+  - btrfs root mount options: `rw,noatime,subvolid=5`
+  - bcachefs root mount options: `rw,noatime`
+- Subvolume mounts (from the primary data filesystem only) to final targets:
+  - Targets: `/var/cache/system`, `/var/cache/etc`, `/var/cache/modules`, `/var/cache/vm-meta`
+  - btrfs subvol options: `-o rw,noatime,subvol={name}`
+  - bcachefs subdir options: `-o rw,noatime,X-mount.subdir={name}`
+- fstab.enabled: default false. When true, zosstorage writes only the four subvolume mount entries, in deterministic target order, using `UUID=` sources for the filesystem; root mounts under `/var/mounts` are excluded.
 
 Report section
 - path: default /run/zosstorage/state.json.
@@ -135,7 +139,7 @@ Minimal single-disk btrfs
 ```yaml
 version: 1
 topology:
-  mode: single
+  mode: btrfs_single
 ```
 
 Dual independent btrfs (two disks)
@@ -186,15 +190,15 @@ Future extensions
 - Multiple topology groups on multi-disk systems
 
 Reference modules
-- [src/types.rs](src/types.rs)
-- [src/config/loader.rs](src/config/loader.rs)
-- [src/cli/args.rs](src/cli/args.rs)
-- [src/orchestrator/run.rs](src/orchestrator/run.rs)
-- [src/partition/plan.rs](src/partition/plan.rs)
-- [src/fs/plan.rs](src/fs/plan.rs)
-- [src/mount/ops.rs](src/mount/ops.rs)
-- [src/report/state.rs](src/report/state.rs)
-- [src/idempotency/mod.rs](src/idempotency/mod.rs)
+- [src/types.rs](../src/types.rs)
+- [src/config/loader.rs](../src/config/loader.rs)
+- [src/cli/args.rs](../src/cli/args.rs)
+- [src/orchestrator/run.rs](../src/orchestrator/run.rs)
+- [src/partition/plan.rs](../src/partition/plan.rs)
+- [src/fs/plan.rs](../src/fs/plan.rs)
+- [src/mount/ops.rs](../src/mount/ops.rs)
+- [src/report/state.rs](../src/report/state.rs)
+- [src/idempotency/mod.rs](../src/idempotency/mod.rs)
 
 Change log
 - v1: Initial draft of schema and precedence rules
diff --git a/docs/SPECS.md b/docs/SPECS.md
index 27a1134..38d012e 100644
--- a/docs/SPECS.md
+++ b/docs/SPECS.md
@@ -3,31 +3,31 @@
 This document finalizes core specifications required before code skeleton implementation. It complements [docs/ARCHITECTURE.md](docs/ARCHITECTURE.md) and [docs/SCHEMA.md](docs/SCHEMA.md), and references the API declarations listed in [docs/API.md](docs/API.md).
 
 Linked modules and functions
-- Logging module: [src/logging/mod.rs](src/logging/mod.rs)
-  - [fn init_logging(opts: &LogOptions) -> Result<()>](src/logging/mod.rs:1)
-- Report module: [src/report/state.rs](src/report/state.rs)
-  - [const REPORT_VERSION: &str](src/report/state.rs:1)
-  - [fn build_report(...) -> StateReport](src/report/state.rs:1)
-  - [fn write_report(report: &StateReport) -> Result<()>](src/report/state.rs:1)
-- Device module: [src/device/discovery.rs](src/device/discovery.rs)
-  - [fn discover(filter: &DeviceFilter) -> Result<Vec<Disk>>](src/device/discovery.rs:1)
-- Partitioning module: [src/partition/plan.rs](src/partition/plan.rs)
-  - [fn plan_partitions(disks: &[Disk], cfg: &Config) -> Result<PartitionPlan>](src/partition/plan.rs:1)
-  - [fn apply_partitions(plan: &PartitionPlan) -> Result<Vec<PartitionResult>>](src/partition/plan.rs:1)
-- Filesystems module: [src/fs/plan.rs](src/fs/plan.rs)
-  - [fn plan_filesystems(disks: &[Disk], parts: &[PartitionResult], cfg: &Config) -> Result<FsPlan>](src/fs/plan.rs:1)
-  - [fn make_filesystems(plan: &FsPlan) -> Result<Vec<FsResult>>](src/fs/plan.rs:1)
-- Mount module: [src/mount/ops.rs](src/mount/ops.rs)
-  - [fn plan_mounts(fs_results: &[FsResult], cfg: &Config) -> Result<MountPlan>](src/mount/ops.rs:1)
-  - [fn apply_mounts(plan: &MountPlan) -> Result<Vec<MountResult>>](src/mount/ops.rs:1)
-  - [fn maybe_write_fstab(mounts: &[MountResult], cfg: &Config) -> Result<()>](src/mount/ops.rs:1)
-- Idempotency module: [src/idempotency/mod.rs](src/idempotency/mod.rs)
-  - [fn detect_existing_state() -> Result<Option<StateReport>>](src/idempotency/mod.rs:1)
-  - [fn is_empty_disk(disk: &Disk) -> Result<bool>](src/idempotency/mod.rs:1)
-- CLI module: [src/cli/args.rs](src/cli/args.rs)
-  - [fn from_args() -> Cli](src/cli/args.rs:1)
-- Orchestrator: [src/orchestrator/run.rs](src/orchestrator/run.rs)
-  - [fn run(ctx: &Context) -> Result<()>](src/orchestrator/run.rs:1)
+- Logging module: [src/logging/mod.rs](../src/logging/mod.rs)
+  - [fn init_logging(opts: &LogOptions) -> Result<()>](../src/logging/mod.rs:1)
+- Report module: [src/report/state.rs](../src/report/state.rs)
+  - [const REPORT_VERSION: &str](../src/report/state.rs:1)
+  - [fn build_report(...) -> StateReport](../src/report/state.rs:1)
+  - [fn write_report(report: &StateReport) -> Result<()>](../src/report/state.rs:1)
+- Device module: [src/device/discovery.rs](../src/device/discovery.rs)
+  - [fn discover(filter: &DeviceFilter) -> Result<Vec<Disk>>](../src/device/discovery.rs:1)
+- Partitioning module: [src/partition/plan.rs](../src/partition/plan.rs)
+  - [fn plan_partitions(disks: &[Disk], cfg: &Config) -> Result<PartitionPlan>](../src/partition/plan.rs:1)
+  - [fn apply_partitions(plan: &PartitionPlan) -> Result<Vec<PartitionResult>>](../src/partition/plan.rs:1)
+- Filesystems module: [src/fs/plan.rs](../src/fs/plan.rs)
+  - [fn plan_filesystems(disks: &[Disk], parts: &[PartitionResult], cfg: &Config) -> Result<FsPlan>](../src/fs/plan.rs:1)
+  - [fn make_filesystems(plan: &FsPlan) -> Result<Vec<FsResult>>](../src/fs/plan.rs:1)
+- Mount module: [src/mount/ops.rs](../src/mount/ops.rs)
+  - [fn plan_mounts(fs_results: &[FsResult], cfg: &Config) -> Result<MountPlan>](../src/mount/ops.rs:1)
+  - [fn apply_mounts(plan: &MountPlan) -> Result<Vec<MountResult>>](../src/mount/ops.rs:1)
+  - [fn maybe_write_fstab(mounts: &[MountResult], cfg: &Config) -> Result<()>](../src/mount/ops.rs:1)
+- Idempotency module: [src/idempotency/mod.rs](../src/idempotency/mod.rs)
+  - [fn detect_existing_state() -> Result<Option<StateReport>>](../src/idempotency/mod.rs:1)
+  - [fn is_empty_disk(disk: &Disk) -> Result<bool>](../src/idempotency/mod.rs:1)
+- CLI module: [src/cli/args.rs](../src/cli/args.rs)
+  - [fn from_args() -> Cli](../src/cli/args.rs:1)
+- Orchestrator: [src/orchestrator/run.rs](../src/orchestrator/run.rs)
+  - [fn run(ctx: &Context) -> Result<()>](../src/orchestrator/run.rs:1)
 
 ---
 
@@ -39,7 +39,7 @@ Goals
 
 Configuration
 - Levels: error, warn, info, debug (default info).
-- Propagation: single global initialization via [fn init_logging](src/logging/mod.rs:1). Subsequent calls must be no-ops.
+- Propagation: single global initialization via [fn init_logging](../src/logging/mod.rs:1). Subsequent calls must be no-ops.
 
 Implementation notes
 - Use tracing and tracing-subscriber.
@@ -57,7 +57,7 @@ Location
 - Default output: /run/zosstorage/state.json
 
 Versioning
-- Include a top-level string field version equal to [REPORT_VERSION](src/report/state.rs:1). Start with v1.
+- Include a top-level string field version equal to [REPORT_VERSION](../src/report/state.rs:1). Start with v1.
 
 Schema example
 
@@ -154,17 +154,17 @@ Default exclude patterns
 - ^/dev/fd\\d+$
 
 Selection policy
-- Compile include and exclude regex into [DeviceFilter](src/device/discovery.rs).
+- Compile include and exclude regex into [DeviceFilter](../src/device/discovery.rs).
 - Enumerate device candidates and apply:
   - Must match at least one include.
   - Must not match any exclude.
   - Must be larger than min_size_gib (default 10).
 - Probing
   - Gather size, rotational flag, model, serial when available.
-  - Expose via [struct Disk](src/device/discovery.rs:1).
+  - Expose via [struct Disk](../src/device/discovery.rs:1).
 
 No eligible disks
-- Return a specific error variant in [enum Error](src/errors.rs:1).
+- Return a specific error variant in [enum Error](../src/errors.rs:1).
 
 ---
 
@@ -181,17 +181,20 @@ Layout defaults
 - Cache partitions (only in ssd_hdd_bcachefs): GPT name zoscache on SSD.
 
 Per-topology specifics
-- single: All roles on the single disk.
-- dual_independent: Each disk gets BIOS boot + ESP + data.
-- ssd_hdd_bcachefs: SSD gets BIOS boot + ESP + zoscache, HDD gets BIOS boot + ESP + zosdata.
+- btrfs_single: All roles on the single disk; data formatted as btrfs.
+- bcachefs_single: All roles on the single disk; data formatted as bcachefs.
+- dual_independent: On each eligible disk (one or more), create BIOS boot (if applicable), ESP, and data.
+- bcachefs_2copy: Create data partitions on two or more disks; later formatted as one multi-device bcachefs spanning all data partitions.
+- ssd_hdd_bcachefs: SSD gets BIOS boot + ESP + zoscache; HDD gets BIOS boot + ESP + zosdata; combined later into one bcachefs.
+- btrfs_raid1: Two disks minimum; data partitions mirrored via btrfs RAID1.
 
 Safety checks
 - Ensure unique partition UUIDs.
-- Verify no pre-existing partitions or signatures. Use blkid or similar via [run_cmd_capture](src/util/mod.rs:1).
-- After partition creation, run udev settle via [udev_settle](src/util/mod.rs:1).
+- Verify no pre-existing partitions or signatures. Use blkid or similar via [run_cmd_capture](../src/util/mod.rs:1).
+- After partition creation, run udev settle via [udev_settle](../src/util/mod.rs:1).
 
 Application
-- Utilize sgdisk helpers in [apply_partitions](src/partition/plan.rs:1).
+- Utilize sgdisk helpers in [apply_partitions](../src/partition/plan.rs:1).
 
 ---
 
@@ -199,34 +202,38 @@ Application
 
 Kinds
 - Vfat for ESP, label ZOSBOOT.
-- Btrfs for data on single and dual_independent.
-- Bcachefs for ssd_hdd_bcachefs (SSD cache, HDD backing).
+- Btrfs for data in btrfs_single, dual_independent, and btrfs_raid1 (with RAID1 profile).
+- Bcachefs for data in bcachefs_single, ssd_hdd_bcachefs (SSD cache + HDD backing), and bcachefs_2copy (multi-device).
 - All data filesystems use label ZOSDATA.
 
 Defaults
-- btrfs: compression zstd:3, raid_profile none unless explicitly set to raid1 in btrfs_raid1 mode.
-- bcachefs: cache_mode promote, compression zstd, checksum crc32c.
+- btrfs: compression zstd:3, raid_profile none unless explicitly set; for btrfs_raid1 use -m raid1 -d raid1.
+- bcachefs: cache_mode promote, compression zstd, checksum crc32c; for bcachefs_2copy use `--replicas=2` (data and metadata).
 - vfat: ESP label ZOSBOOT.
 
 Planning and execution
-- Decide mapping of [PartitionResult](src/partition/plan.rs:1) to [FsSpec](src/fs/plan.rs:1) in [plan_filesystems](src/fs/plan.rs:1).
-- Create filesystems in [make_filesystems](src/fs/plan.rs:1) through wrapped mkfs tools.
-- Capture resulting identifiers (fs uuid, label) in [FsResult](src/fs/plan.rs:1).
+- Decide mapping of [PartitionResult](../src/partition/plan.rs:1) to [FsSpec](../src/fs/plan.rs:1) in [plan_filesystems](../src/fs/plan.rs:1).
+- Create filesystems in [make_filesystems](../src/fs/plan.rs:1) through wrapped mkfs tools.
+- Capture resulting identifiers (fs uuid, label) in [FsResult](../src/fs/plan.rs:1).
 
 ---
 
 ## 6. Mount scheme and fstab policy
 
-Scheme
-- per_uuid under /var/cache: directories named as filesystem UUIDs.
+Runtime root mounts (all data filesystems)
+- Each data filesystem is root-mounted at `/var/mounts/{UUID}` (runtime only).
+- btrfs root mount options: `rw,noatime,subvolid=5`
+- bcachefs root mount options: `rw,noatime`
 
-Mount options
-- btrfs: ssd when non-rotational underlying device, compress from config, defaults otherwise.
-- vfat: defaults, utf8.
+Final subvolume/subdir mounts (from the primary data filesystem)
+- Create or ensure subvolumes named: `system`, `etc`, `modules`, `vm-meta`
+- Mount targets: `/var/cache/system`, `/var/cache/etc`, `/var/cache/modules`, `/var/cache/vm-meta`
+- btrfs options: `-o rw,noatime,subvol={name}`
+- bcachefs options: `-o rw,noatime,X-mount.subdir={name}`
 
-fstab
+fstab policy
 - Disabled by default.
-- When enabled, [maybe_write_fstab](src/mount/ops.rs:1) writes deterministic entries sorted by target path.
+- When enabled, [maybe_write_fstab](../src/mount/ops.rs:1) writes only the four final subvolume/subdir entries using `UUID=` sources, in deterministic target order. Root mounts under `/var/mounts` are excluded.
 
 ---
 
@@ -235,20 +242,23 @@ fstab
 Signals for already-provisioned system
 - Expected GPT names found: zosboot, zosdata, and zoscache when applicable.
 - Filesystems with labels ZOSBOOT for ESP and ZOSDATA for all data filesystems.
-- When consistent with selected topology, [detect_existing_state](src/idempotency/mod.rs:1) returns a StateReport and orchestrator exits success without changes.
+- When consistent with selected topology, [detect_existing_state](../src/idempotency/mod.rs:1) returns a StateReport and orchestrator exits success without changes.
 
 Disk emptiness
-- [is_empty_disk](src/idempotency/mod.rs:1) checks for absence of partitions and FS signatures before any modification.
+- [is_empty_disk](../src/idempotency/mod.rs:1) checks for absence of partitions and FS signatures before any modification.
 
 ---
 
 ## 8. CLI flags and help text outline
 
-Flags mirrored by [struct Cli](src/cli/args.rs:1) parsed via [from_args](src/cli/args.rs:1)
+Flags mirrored by [struct Cli](../src/cli/args.rs:1) parsed via [from_args](../src/cli/args.rs:1)
 - --config PATH
 - --log-level LEVEL    error | warn | info | debug
 - --log-to-file
 - --fstab              enable fstab generation
+- --show               print preview JSON to stdout (non-destructive)
+- --report PATH        write preview JSON to file (non-destructive)
+- --apply              perform partitioning, filesystem creation, and mounts (DESTRUCTIVE)
 - --force              present but returns unimplemented error
 
 Kernel cmdline
@@ -257,7 +267,7 @@ Kernel cmdline
 Help text sections
 - NAME, SYNOPSIS, DESCRIPTION
 - CONFIG PRECEDENCE
-- TOPOLOGIES: single, dual_independent, ssd_hdd_bcachefs, btrfs_raid1
+- TOPOLOGIES: btrfs_single, bcachefs_single, dual_independent, bcachefs_2copy, ssd_hdd_bcachefs, btrfs_raid1
 - SAFETY AND IDEMPOTENCY
 - REPORTS
 - EXIT CODES: 0 success or already_provisioned, non-zero on error
@@ -267,9 +277,10 @@ Help text sections
 ## 9. Integration testing plan (QEMU KVM)
 
 Scenarios to scaffold in [tests/](tests/)
-- Single disk 40 GiB virtio: validates single topology end-to-end smoke.
-- Dual NVMe 40 GiB each: validates dual_independent topology.
-- SSD NVMe + HDD virtio: validates ssd_hdd_bcachefs topology.
+- Single disk 40 GiB virtio: validates btrfs_single topology end-to-end smoke.
+- Dual NVMe 40 GiB each: validates dual_independent topology (independent btrfs per disk).
+- SSD NVMe + HDD virtio: validates ssd_hdd_bcachefs topology (bcachefs with SSD cache/promote, HDD backing).
+- Three disks: validates bcachefs_2copy across data partitions using `--replicas=2`.
 - Negative: no eligible disks, or non-empty disk should abort.
 
 Test strategy
@@ -281,7 +292,7 @@ Test strategy
 Artifacts to validate
 - Presence of expected partition GPT names.
 - Filesystems created with correct labels.
-- Mountpoints under /var/cache/<UUID> when running in a VM.
+- Runtime root mounts under `/var/mounts/{UUID}` and final subvolume targets at `/var/cache/{system,etc,modules,vm-meta}`.
 - JSON report validates against v1 schema.
 
 ---
diff --git a/docs/adr/0001-modular-workflow.md b/docs/adr/0001-modular-workflow.md
index 03f98ad..9f12efc 100644
--- a/docs/adr/0001-modular-workflow.md
+++ b/docs/adr/0001-modular-workflow.md
@@ -47,14 +47,14 @@ Consequences
 
 Implementation Notes
 - Region markers have been added to key modules:
-  - [src/config/loader.rs](src/config/loader.rs)
-  - [src/orchestrator/run.rs](src/orchestrator/run.rs)
-  - [src/cli/args.rs](src/cli/args.rs)
-  - [src/device/discovery.rs](src/device/discovery.rs)
-  - [src/partition/plan.rs](src/partition/plan.rs)
-  - [src/fs/plan.rs](src/fs/plan.rs)
-  - [src/mount/ops.rs](src/mount/ops.rs)
-  - [src/report/state.rs](src/report/state.rs)
+  - [src/config/loader.rs](../src/config/loader.rs)
+  - [src/orchestrator/run.rs](../src/orchestrator/run.rs)
+  - [src/cli/args.rs](../src/cli/args.rs)
+  - [src/device/discovery.rs](../src/device/discovery.rs)
+  - [src/partition/plan.rs](../src/partition/plan.rs)
+  - [src/fs/plan.rs](../src/fs/plan.rs)
+  - [src/mount/ops.rs](../src/mount/ops.rs)
+  - [src/report/state.rs](../src/report/state.rs)
 - Remaining modules will follow the same pattern as needed (e.g., util, idempotency, main/lib if helpful).
 
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