Synology DSM: Administration and btrfs Recovery

Operate Synology NAS appliances over SSH: package and service control, storage stack inspection, snapshots and backups, and recovery of btrfs volumes that will not mount.

DSM is a Linux appliance with a heavily modified btrfs and a userspace that regenerates its own config. Two facts drive most of this skill: DSM's btrfs on-disk format is newer than the btrfs-progs DSM ships and diverges from mainline, so stock tools report healthy volumes as corrupt; and DSM regenerates /etc/fstab and package state at boot, so hand edits do not survive.

Target versions: see references/versions.md (verified per the receipt date in that file). Do not restate version numbers here.

• Userspace btrfs on the appliance is old (v4.0 on DSM 7.1 avoton). Check with btrfs --version before assuming a subcommand exists

DSM 7.1.x and earlier do not appear in current advisories' fixed-version lists; treat them as unpatched. That is a reason to plan an upgrade, not to run one on a unit with a broken volume.