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Take automatic snapshots of cephfs file systems

Take automatic snapshots of cephfs file systems

Cephfs is a great tool. It enables users to store and share files while taking advantage of the granularity and performance of Ceph. One of the reasons why I’m using it is the possibility of being used on erasure coded (slow disk) pools and cached on fast ssd disks.

Big amounts of data can be stored and live snapshots can be taken so remote backups can be easily performed. Those snapshots have helped me to restore specific files or directories to specific points in time in a transparent and easy way, multiple times.

Taking a manual snapshot is easy: you’ll find a “.snap” hidden directory inside any directory of your (cephfs) file system. You can just “mkdir something” inside the .snap directory and you’ll have a full snapshot called “something”. To remove a snapshot, simply use the ‘rmdir’ command and CephFS will delete and trim the space as soon as possible.

To be able to perform it automatically, I’ve adaped a script called “btrfs-snp”, that I generally use to snapshot a BTRFS file system, and created "cephfs-snp".

Using cephfs-snp is quite easy:

# cephfs-snp
Usage: cephfs-snp <dir> (<tag>) (<limit>) (<seconds>)

  dir     │ create snapshot of <dir>
  tag     │ name the snapshot <tag>_<timestamp>
  limit   │ keep <limit> snapshots with this tag. 0 to disable
  seconds │ don't create snapshots before <seconds> have passed from last with this tag. 0 to disable

You can just ask to perform a snapshot or specify more options to have a more granular control of the snapshots created.

It becomes quite interesting when used with cron:

# cat > /etc/cron.hourly/cephfs-snp <<EOF
/usr/local/sbin/$BIN /home hourly  24 3600
/usr/local/sbin/$BIN /home daily    7 86400
/usr/local/sbin/$BIN /home weekly   4 604800
/usr/local/sbin/$BIN /     weekly   4 604800
/usr/local/sbin/$BIN /home monthly 12 2592000
chmod +x /etc/cron.hourly/cephfs-snp

For more information, you can have a look here:

Have fun!

See also