Storage and COW

Storage and COW

Blueprint volumes use cow, ro, or rw intent:

• cow creates an isolated writable instance view from clean source content.
• ro protects the source through a private writable instance view; it is not a strict read-only bind mount.
• rw intentionally links persistent single-writer instance state to a shared source and receives no rollback or backup from SLS-LITE.

With storage.strategy: auto, SLS-LITE prefers:

1. Reflink
2. Eligible Btrfs snapshot
3. Kernel OverlayFS
4. Rootless fuse-overlayfs
5. Portable copy

storage.auto_priority can replace that order with any non-empty unique subset. It is authoritative: omitted strategies are not probed or selected, and omitting copy disables portable fallback. storage.copy_parallelism retains the conservative CPU-based automatic limit by default or accepts a bounded explicit worker count.

Each native choice requires a successful probe on the actual configured path. An operator snapshot helper is explicit-only and never auto-discovered. Missing privileges, /dev/fuse, filesystem support, or helper access do not justify weakening a hosting provider's normal security profile; auto uses portable copy instead.

Always budget enough disk for portable fallback and keep source worlds unchanged while preparation is running.

Canonical reference: Blueprint Volumes. Operational probes and recovery are documented in Operations.