ZFS: Setting Up Automatic Snapshots

I considered writing a script to take care of this. Luckily, before I got too far down that rabbit hole, I stumbled upon Bryan Drewery’s zfstools on GitHub.

The zfstools installs a few Ruby (programming language) scripts that make managing automatic ZFS snapshots really easy. While you can customize the snapshot retention, the defaults will probably serve you well.

The default snapshot schedule is to snapshot your selected ZFS datasets:

• every 15 minutes – keeping the last 4 quarter-hour snapshots
• every hour – keeping the last 24 hourly snapshots
• every day – keeping 7 daily snapshots
• every week – keeping 4 weekly snapshots
• every month – keeping 12 monthly snapshots

The setup is easy on FreeBSD. It only takes 3 steps:

1. install the scripts
2. turn on auto snapshotting
3. update the /etc/crontab file

Start by installing zfstools from the FreeBSD package system:

$ sudo pkg install zfstools

Then, determine which ZFS datasets to automatically be snapshot. Turn on auto-snapshotting for these ZFS datasets:

$ sudo zfs set com.sun:auto-snapshot=true ZPOOL/DATASET

Where ZPOOL is the name of the zpool and where DATASET is the name of the ZFS dataset that you want to be automatically snapshot.

Next, it is time to update your machine’s /etc/crontab file to run the script. If you have never touched your /etc/crontab file before, take a moment to read the manual page for this magical file:

$ man 5 crontab

Next, copy the 5 crontab lines from https://github.com/bdrewery/zfstools README.md file. Look for the lines that have tons of asterisks – the manual page listed above explains what these asterisks and the rest of the fields represent.

Also, make sure the /etc/crontab PATH line contains the directories where ruby and zfs-auto-snapshot live. On my machine these were:

• /usr/local/bin/
• /usr/local/sbin/

You can figure out what yours are by typing:

$ which ruby

and

$ which zfs-auto-snapshot

The PATH line in my /etc/crontab file ended up looking like this:

PATH=/etc:/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin

Wait for the clock to pass the quarter hour then look for the automatic snapshots:

$ zfs list -t snapshot

You will see automatic snapshots start to pile up.