Re: restic backup with btrfs /

[Mark Harmstone <mark@harmstone.com>]

On 28/06/2025 6.33 pm, Ulli Horlacher wrote:
> restic (https://restic.net/) is a great backup tool but has some
> limitations or design flaws: one is, it believes that any subvolume is on a
> different filesystem. This means: "restic backup --one-file-system /" will
> only backup the root subvolume, but no other subvolumes like /home
> /var/spool etc...
> 
> One has to add every subvolume to the argument list. Bad if you
> create new subvolumes and forget to update the backup cronjob.
> When you later need to restore a file, there will be none...

This is a bug in Restic that needs to be fixed, though they may not see it that
way. The issue is that btrfs uses a different device number for each subvolume -
I believe this is because subvols can share inode numbers, and VFS gets confused
otherwise.

The same behaviour can be seen with rsync, which restic might well use
internally.

> My idea is now: I do not backup the original /, but do:
> 
> mount --bind / /backup/restic
> restic backup /backup/restic
> umount /backup/restic
> 
> Next evolution step:
> I could recursivly mount-bind other filesystems into /backup/restic/
> For example:
> 
> mount --bind /local /backup/restic/local
> mount --bind /data /backup/restic/ldata

This is unlikely to work, as bind mounts will also be seen as different
filesystems.

> That I would have a "all in one backup".
> 
> What do you think of this idea?
>