SnapBtr is a small script i (Helge Jensen <firstname.lastname@example.org>) hacked together.
snapbtr is a small utility that keeps snapshots of btrfs filesystems.
You can run it regularly (for example in a small script in cron.hourly), or once in a while, to maintain an "interesting" (see below) set of snapshots (backups). You may manually add or remove snapshots as you like, use 'snapbtr.DATE_FORMAT' (in GMT) as snapshot-name.
It will keep at most --target-backups snapshots and ensure that --target-freespace is available on the file-system by selecting snapshots to remove.
Using --keep-backups, you can ensure that at least some backups are kept, even if --target-freespace cannot be satisfied.
snapnbtr will keep backups with exponentially increasing distance as you go back in time. It does this by selecting snapshots to remove as follows.
The snapshots to remove is selected by "scoring" each space between snapshots, (newer,older). snapbtr will remove the older of the two snapshots in the space that have the lowest score.
The scoring mechanism integrates e^x from (now-newer) to (now-older) so, new pairs will have high value, even if they are tightly packed, while older pairs will have high value if they are far apart.
The mechanism is completely self-contained and you can delete any snapshot manually or any files in the snapshots.
I personally install snapbtr.py into /var/backups/snapbtr which is only accessible to root and run it from a small script in cron.hourly. I also install the kernel-nfs-server package and nfs-export /var/backups/snapbtr in /etc/exports:
and mount it at /mnt/restore, in /etc/fstab:
localhost:/var/backups/snapbtr/ /mnt/restore nfs _netdev,nosuid,rsize=8192,hard,intr,ro 0 2
That way, all users can use the backups in /mnt/restore, but cannot exploit security-bugs or tamper with the content.
Source: Media:snapbtr.txt (Wiki does not allow .py uploads)