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I'm using btrfs-sxbackup to create local snapshots. It creates a technical subvolume in /.sxbackup and creates readonly snapshots in its subfolder. All subvolumes are automatically mounted when OS boots, nothing needed to be specified in fstab.

This one time I tried to restore a snapshot:

btrfs subvol snapshot /.sxbackup/sx-20190308-070926-utc /.before-5.0
btrfs subvol set-default /.before-5.0

Upon reboot the technical subvolume /.sxbackup/ is not mounted. Now every time I have to mount it manually.

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On BTRFS, subvolumes form the "snapshot barrier." Meaning, when you snapshot a subvolume which contains subvolumes, the nested subvolumes are not included in the snapshot.

But care must be taken when snapshots should be made (nested subvolumes are not part of a snapshot, and as of now, there are no recursive snapshots)... - source https://btrfs.wiki.kernel.org/index.php/SysadminGuide#Nested

If you check your snapshots in /.sxbackup you'll find that none of them contain the .sxbackup subvolume.

To make the snapshots available in a consistent fashion, consider adding a read-only mount-point of the .sxbackup subvolume to some other place on the filesystem. For example:

/etc/fstab

/dev/sd* /mnt/snapshots btrfs ro,subvol=/.sxbackup 0 0

The above example mounts the .sxbackup subvolume at /mnt/snapshots regardless of which subvolume is the default.

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  • I'm starting to think that installing OS to the top-level subvolume was a bad idea
    – basin
    Commented Mar 13, 2019 at 15:37
  • Yeah... a flat layout provides more flexibility.
    – Emmanuel Rosa
    Commented Mar 14, 2019 at 4:29

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