a survey of FreeBSD ZFS snapshot automation tools
Why automatically snapshot filesystems? Because snapshots let you magically fall back to older versions of files and even the operating system. Taking a manual snapshot before a system upgrade is laudable, but you need to easily recover files when everything goes bad. So I surveyed my Twitter followers to see what FreeBSD ZFS snapshot automation tools they use.
A few people use custom shell scripts of varying reliability and flexibility. I’m not going to write my own shell script. The people who write canned snapshot rotation tools have solved this problem, and I have no desire to re-solve it myself.
One popular choice was sysutils/zfs-snapshot-mgmt. This lets you create snapshots as often as once per minute, and retain them as long as you desire. Once a minute is a bit much for me. You can group snapshot creation and deletion pretty much arbitrarily, letting you keep, say, 867 per-minute snapshots, 22 every-seven-minute snapshots, and 13 monthlies, if that’s what you need. This is the Swiss army knife of ZFS snapshot tools. One possible complication with zfs-snapshot-mgmt is that it is written in Ruby and configured in YAML. If you haven’t seen YAML yet, you will–it’s an increasingly popular configuration syntax. My existing automation is all in shell and Perl, however. I added Python for Ansible. Adding yet another interpreter to all of my ZFS systems doesn’t thrill me. Ruby is not a show-stopper, but it doesn’t thrill me. The FreeBSD port is outdated, however–the web site referenced by the port says that the newest code, with bug fixes, is on github. If you’re looking for a FreeBSD porting project, this would be an easy one.
The zfs-periodic web page is down. NEC Energy Solutions owns the domain, so I’m guessing that the big corporate overlord claimed the blog and the site isn’t not coming back. The code still lives at various mirrors, however. zfs-periodic is tightly integrated with FreeBSD’s periodic system, and can automatically create and delete hourly, daily, monthly, and weekly snapshots. It appears to be the least flexible of the snapshot systems, as it runs with periodic. If you want to take your snapshots at a time that periodic doesn’t run, too bad. I don’t get a very good feeling from zfs-periodic–if the code had an owner, it would have a web site somewhere.
sysutils/zfsnap can do hourly, daily, weekly, and monthly snapshots. It’s designed to run from periodic(8) or cron(8), and is written in /bin/sh.
sysutils/zfstools includes a clone of OpenSolaris’ automatic snapshotting tools. I no longer run OpenSolaris-based systems, except on legacy servers that I’m slowly removing, but I never know what the future holds around the dayjob. (I’m waiting for the mission-critical Xenix deployment, I’m sure it’s not far off.) This looks highly flexible, being configured by a combination of cron scripts and ZFS attributes, and can snapshot every 15 minutes, hour, day, week, and month. It’s written in Ruby (yet another scripting language on my system? Oh, joy. Joy and rapture.) On the plus side, the author of zfstools is also a FreeBSD committer, so I can expect him to keep the port up to date.
In doing this survey I also came across sysutils/freebsd-snapshot, a tool for automatically scheduling and automounting UFS snapshots. While I’m not interested in UFS snapshots right now, this is certainly worth remembering.
So, which ones will I try? I want a tool that’s still supported and has some flexibility. I want a FreeBSD-provided package of the current version of the software. I’m biased against adding another scripting language to my systems, but that’s not veto-worthy.
If I want compatibility with OpenSolaris, I’ll use zfstools. I get another scripting language, yay!
If I don’t care about OpenSolaris-derived systems, zfsnap is the apparent winner.
Of course, I won’t know which is better until I try both… which will be the topic of a couple more blogs.
UPDATE, 07-31-2014: I screwed up my research on zfsnap. I have rewritten that part of the article, and my conclusions. My apologies — that’s what happens when you try to do research after four hours sleep. Thanks to Erwin Lansing for pointing it out.
(“Gee, I’m exhausted. Better not touch any systems today. What shall I do? I know, research and a blog post!” Sheesh.)