We've been moving from OpenBSD to FreeBSD for firewalls . One advantage of this is giving us a mirrored ZFS pool for the machine's filesystems ; we have a lot of experience operating ZFS and it's a simple, reliable, and fully supported way of getting mirrored system disks on important machines. ZFS has checksums and you want to periodically 'scrub' your ZFS pools to verify all of your data (in all of its copies) through these checksums ( ideally relatively frequently ). All of this is part of basic ZFS knowledge, so I was a little bit surprised to discover that none of our FreeBSD machines had ever scrubbed their root pools, despite some of them having been running for months.

It turns out that while FreeBSD comes with a configuration option to do periodic ZFS scrubs, the option isn't enabled by default (as of FreeBSD 14.3). Instead you have to know to enable it, which admittedly isn't too hard to find once you start looking.

FreeBSD has a general periodic(8) system for triggering things on a daily, weekly, monthly, or other basis. As covered in the manual page, the default configuration for this is in /etc/defaults/periodic.conf and you can override things by creating or modifying /etc/periodic.conf. ZFS scrubs are a 'daily' periodic setting, and as of 14.3 the basic thing you want is an /etc/periodic.conf with:

# Enable ZFS scrubs
daily_scrub_zfs_enable="YES"

FreeBSD will normally scrub each pool a certain number of days after its previous scrub (either a manual scrub or an automatic scrub through the periodic system). The default number of days is 35, which is a bit high for my tastes, so I suggest that you shorten it, making your periodic.conf stanza be:

# Enable ZFS scrubs
daily_scrub_zfs_enable="YES"
daily_scrub_zfs_default_threshold="14"

There are other options you can set that are covered in /etc/defaults/periodic.conf.

(That the daily automatic scrubs happen some number of days after the pool was last scrubbed means that you can adjust their timing by doing a manual scrub. If you have a bunch of machines that you set up at the same time, you can get them to space out their scrubs by scrubbing one a day by hand, and so on.)

Looking at the other ZFS periodic options, I might also enable the daily ZFS status report, because I'm not certain if there's anything else that will alert you if or when ZFS starts reporting errors:

# Find out about ZFS errors?
daily_status_zfs_enable="YES"

You can also tell ZFS to TRIM your SSDs every day. As far as I can see there's no option to do the TRIM less often than once a day; I guess if you want that you have to create your own weekly or monthly periodic script (perhaps by copying the 801.trim-zfs daily script and modifying it appropriately). Or you can just do 'zpool trim ...' every so often by hand.