Scrub of one external USB drive took 2days-3hours. Scrub of the second one is still going...
No, the purpose of scrub is explicitly to look at problems with the disk that happen "spontaneously". Two examples of such problems are mechanical damage to the platter and head (scratches, foreign objects, moguls in the lubricant), and off-track writes (where data should have been to one location, and ends up in a different location). These problems don't just happen to the data that is being written.Well I was doubting if it only checked the "meanwhile changed datablocks".
Don't you mean /etc/periodic.confI've no idea what "best practices" for zfs scrub are, but I'll note that the default of every 35 days has served me well for many years now. FreeBSD handles this via the periodic script /etc/periodic/daily/800.scrub-zfs which gets its default values from /etc/defaults/periodic.conf:
If you want to change some of them, you should pout them in the /etc/rc.conf file.Code:root@kg-core2# grep scrub_zfs /etc/defaults/periodic.conf daily_scrub_zfs_enable="NO" daily_scrub_zfs_pools="" # empty string selects all pools daily_scrub_zfs_default_threshold="35" # days between scrubs #daily_scrub_zfs_${poolname}_threshold="35" # pool specific threshold
/etc/defaults/periodic.conf contains the defaults, just as /etc/defaults/rc.conf contains a bunch of defaults too. Those settings can be overruled by setting them in /etc/periodic.conf and /etc/rc.conf respectively.Don't you mean /etc/periodic.conf