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.