Recently i replaced a HDD on a Backup-Server on a customer site with a bigger one. Its a freenas box running on a HP SE326M1*.

While ZFS was replacing the drive a major power outage occured.

Was no big Problem - the box started again and the resilver too.

Today i found something interesting: another drive got the resilvering status too. But there are no read/write/cksum-errors in zpool status -v

  pool: Tank
 state: ONLINE
status: One or more devices is currently being resilvered.  The pool will
        continue to function, possibly in a degraded state.
action: Wait for the resilver to complete.
  scan: resilver in progress since Sat Mar  4 15:37:53 2017
        3.41T scanned out of 4.51T at 24.7M/s, 13h3m to go
        302G resilvered, 75.43% done

    NAME                                            STATE     READ WRITE CKSUM
    Tank                                            ONLINE       0     0     0
      raidz2-0                                      ONLINE       0     0     0
        gptid/ad81fb87-96b5-11e6-af9c-d8d385e6539a  ONLINE       0     0     0
        gptid/b30f664d-96b5-11e6-af9c-d8d385e6539a  ONLINE       0     0     0
        gptid/09b6b651-ff29-11e6-9a6a-d8d385e6539a  ONLINE       0     0     0  (resilvering) <-- drive was replaced
        gptid/beb62f74-96b5-11e6-af9c-d8d385e6539a  ONLINE       0     0     0
        gptid/c2c97ff3-96b5-11e6-af9c-d8d385e6539a  ONLINE       0     0     0
      raidz2-1                                      ONLINE       0     0     0
        gptid/41b1a629-9785-11e6-894c-d8d385e6539a  ONLINE       0     0     0
        gptid/4756cd8e-9785-11e6-894c-d8d385e6539a  ONLINE       0     0     0
        gptid/508e74c7-9785-11e6-894c-d8d385e6539a  ONLINE       0     0     0
        gptid/575939b3-9785-11e6-894c-d8d385e6539a  ONLINE       0     0     0  (resilvering) <-- drive in question
        gptid/5d914967-9785-11e6-894c-d8d385e6539a  ONLINE       0     0     0

errors: No known data errors

The status "(resilvering)" appeared in the last hours - while the resilver of the first drive was in progress.

Is there any way to determie why the second drive is resilvered too? Why ZFS is showing the resilver status on gptid/575939b3-9785-11e6-894c-d8d385e6539a regardless of errors shown in zpool status?


*The HP-Server has a P410 raid controller in write-throug-mode. Every drive is configured as its own Raid-0

  • Maybe the disk was dropped by the controller? Do you have a log where such events are recorded? – user121391 Mar 7 '17 at 7:53
  • there were messages from the controller regarding drive temperature. Sometimes the temp on one drive triggers a warning. But after a minute it returns to normal. But i have seen this messages since setup. Port naming is strange (Port 1I) - could be the drive in question. Will replace it when expansion of raidz2-0 has finished. – Martin Seitl Mar 7 '17 at 8:30
  • Well all I’ve is that this means the drive was absent, so pretty much what user121391 said. I’m not that familiar with FreeBSD, but surely there’s some sort of log facility for kernel messages? Look for messages about your disk. You’ll probably have to look for the real device name (like ada6 or whatever). – Daniel B Mar 7 '17 at 9:01
  • I searched the logs, but there was nothing about disk error or detach/reattach. Only two entries from autosnap.py (snapshot destroy and snapshot create) were in the timeframe. Could snapshots trigger a resilver on a nearly unaffected disk without an error? – Martin Seitl Mar 7 '17 at 21:40
  • Aside from bugs, no. Snapshots operate on file systems, not on disks. Additionally, creating the snap is a simple IO operation like any other. Afterwards the snap does only change if the file system is changed (if additional IO happens), so you would have to look at any IO in the time period. – user121391 Mar 10 '17 at 12:31

It happend again and this time i have the logs. it turns out that user121391 was totally right and the drive in question had an "unretryable" error.

Mar 12 08:22:14 freenas ciss0: *** Fatal drive error, Port=1I Box=1 Bay=14
Mar 12 08:22:14 freenas ciss0: (da9:ciss0:0:9:0): READ(10). CDB: 28 00 1b 50 ff 98 00 00 08 00 
Mar 12 08:22:14 freenas FATAL I/O ERROR on logical drive 9 (), SCSI port 0 ID 21
Mar 12 08:22:14 freenas (da9:ciss0:0:9:0): CAM status: SCSI Status Error
Mar 12 08:22:14 freenas (da9:ciss0:0:9:0): SCSI status: Check Condition
Mar 12 08:22:14 freenas (da9:ciss0:0:9:0): SCSI sense: MEDIUM ERROR asc:11,0 (Unrecovered read error)
Mar 12 08:22:14 freenas (da9:ciss0:0:9:0): Error 5, Unretryable error

It seems that the raid-controller reattached the drive after this error and this triggered the resilver.

  • Glad you could solve it! Thanks for reporting back. Out of curiosity, what log file was this exactly? (not having used BSD much myself, it could be useful to know for the future) – user121391 Mar 16 '17 at 7:43
  • 1
    It is a FreeNAS 9 and there is an option to show console-messages in the web-interface. Unfortunately i couldn't find a logfile for that - but since the web interface was open while it happend it showed up there. – Martin Seitl Mar 16 '17 at 8:41

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