I have a self-built FreeNAS system, which uses 4 HDD in one ZFS pool purely for storage, and 2 mirrored 16GB USB memory sticks in a ZFS mirror for booting from. It is stable and has been running for around 8 months. However, the overnight emails are usually along these lines:
Checking status of zfs pools: NAME SIZE ALLOC FREE EXPANDSZ FRAG CAP DEDUP HEALTH ALTROOT freenas-boot 14.5G 1.67G 12.8G - - 11% 1.00x ONLINE - volume1 7.25T 457G 6.80T - 2% 6% 1.00x ONLINE /mnt
pool: freenas-boot state: ONLINE status: One or more devices has experienced an unrecoverable error. An attempt was made to correct the error. Applications are unaffected. action: Determine if the device needs to be replaced, and clear the errors using 'zpool clear' or replace the device with 'zpool replace'. see: http://illumos.org/msg/ZFS-8000-9P scan: scrub repaired 232K in 0h6m with 0 errors on Sun Oct 23 03:51:22 2016 config:
NAME STATE READ WRITE CKSUM freenas-boot ONLINE 0 0 0 mirror-0 ONLINE 0 0 0 gptid/253f05a3-be26-11e5-8d9c-d05099c04470 ONLINE 0 0 1 gptid/879584e0-bfb0-11e5-ba20-d05099c04470 ONLINE 0 0 9
errors: No known data errors
The checksum errors will occasionally increase, then when I perform a normal FreeNAS update, will all reset back to 0 again, whereupon the process will repeat, with the checksum errors creeping up now and again.
I've seen nothing to indicate that the HDDs themselves are having any faults, and I download the FreeNAS config to an external backup location when I make changes, so I should be able to reinstall on a new flash drive if necessary.
All that said, how concerned should I be about these checksum errors?