Thursday, April 03, 2014

Home NAS - Data Corruption

I value my personal pictures so I store them on a home NAS which is running Solaris/ZFS. The server has two data disks mirrored. It's been running perfectly fine for the last two years but recently one of the disk drives returned corrupted data during ZFS scrub. If it wasn't for ZFS I probably wouldn't even know that some pixels are wrong... or perhaps that some pictures are missing... This is exactly why I've used ZFS on my home NAS.

# zpool status vault
  pool: vault
 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'.
  scan: scrub repaired 256K in 3h54m with 0 errors on Tue Mar 11 17:34:22 2014

        NAME        STATE     READ WRITE CKSUM
        vault       ONLINE       0     0     0
          mirror-0  ONLINE       0     0     0
            c4t1d0  ONLINE       0     0     2
            c5t0d0  ONLINE       0     0     0

errors: No known data errors

1 comment:

Anubis said...

So does ZFS fix the bad data by writing it to a new sector on the mirror disk, or does it just re-write it in-place?

If it's re-written in-place, does anything check the previous data location for the presence of bad sectors?