Snapshots allow you to copy the state of your zpool at a given instance. This
can be useful in many ways. For instance, if you delete a file that you still
want and you have a snapshot of a time when you had the file you can go
retrieve it. Snapshots are cheap to make, so one is encouraged to make them
often. Before setting up automated snapshots I had only ever made two
snapshots. You can view your snapshots with
zfs list -t snapshot:
In this output
fresh was made when I had just made the zpool and
home_restored was made just after I had restored my home directory from
backup to the zpool.
This is a great start, but we don’t want to just rely on making snapshots by hand. It would be more useful if we have some automated system for taking snapshots. Thankfully, such tools already exists. I am going to install zfs-auto-snapshot-git from the AUR, which is from the folks at zfsonlinux. Upon installation we will see the following output:
This automated system used to use cronjobs to run the included
zfs-auto-snapshot script, but it looks like back in September 2014 the
cronjobs were swapped out for systemd
If you are unfamiliar with systemd timers (like I was when I came across this)
they are simply timers which control a systemd service. You can view active
systemctl list-timers. You will notice that when we installed
zfs-auto-snapshot-git a set of
.timer files were installed
.timer pair is for a time interval for making snapshots.
Let’s take a look at the hourly pair.
As you can see the files are fairly simple.
Persistent=true in the
file will run the job if we happened to miss the last time it should have run,
say if your computer was off or suspended, like an anacron job. The
file just runs the the
zfs-auto-snapshot script, labels it as
keeps 24 snapshots. The
// refers to all storage nodes.
To enable automated snapshots we will first have to set an auto-snapshot parameter as stated in the installation output:
Then we just have to enable whatever timer(s) we want, this will enable an automated backup at that interval:
You can always manually run
zfs-auto-snapshot which will produce a single
backup. I have setup an hourly, daily, weekly and monthly auto-snapshot which
has been running now for two months and everything seems to be going smoothly.
If you’d like to read more about snapshots I’d suggest checking out this page: https://pthree.org/2012/12/19/zfs-administration-part-xii-snapshots-and-clones/.