ZFS v28 on -STABLE not using hot spare

[Matt Burke]

Over the holidays one of the disks on a server has failed, but despite
configuring a hot spare, ZFS hasn't used it for some reason. Can anyone
shed some light on what I might have mis-configured to break the hot-spare
functionality?


[root at x ~]# uname -a
FreeBSD x 8.2-STABLE FreeBSD 8.2-STABLE #4: Mon Dec  5 12:43:58 GMT 2011
  root at x:/usr/obj/usr/src/sys/x  amd64


[root at x ~]# more /usr/src/sys/amd64/conf/x
include         GENERIC
ident           x

options         GEOM_STRIPE
options         ROUTETABLES=4


[root at x ~]# zpool status -v
  pool: data
 state: DEGRADED
status: One or more devices are faulted in response to persistent errors.
	Sufficient replicas exist for the pool to continue functioning in a
	degraded state.
action: Replace the faulted device, or use 'zpool clear' to mark the device
	repaired.
 scan: none requested
config:

	NAME         STATE     READ WRITE CKSUM
	data         DEGRADED     0     0     0
	  mirror-0   ONLINE       0     0     0
	    mfid0    ONLINE       0     0     0
	    mfid14   ONLINE       0     0     0
	  mirror-1   ONLINE       0     0     0
	    mfid1    ONLINE       0     0     0
	    mfid15   ONLINE       0     0     0
	  mirror-2   DEGRADED     0     0     0
	    mfid2    ONLINE       0     0     0
	    mfid16   FAULTED      0   931     0  too many errors
	  mirror-3   ONLINE       0     0     0
	    mfid3    ONLINE       0     0     0
	    mfid17   ONLINE       0     0     0
	  mirror-4   ONLINE       0     0     0
	    mfid4    ONLINE       0     0     0
	    mfid18   ONLINE       0     0     0
	  mirror-5   ONLINE       0     0     0
	    mfid5    ONLINE       0     0     0
	    mfid19   ONLINE       0     0     0
	  mirror-6   ONLINE       0     0     0
	    mfid6    ONLINE       0     0     0
	    mfid20   ONLINE       0     0     0
	  mirror-7   ONLINE       0     0     0
	    mfid7    ONLINE       0     0     0
	    mfid21   ONLINE       0     0     0
	  mirror-8   ONLINE       0     0     0
	    mfid8    ONLINE       0     0     0
	    mfid22   ONLINE       0     0     0
	  mirror-9   ONLINE       0     0     0
	    mfid9    ONLINE       0     0     0
	    mfid23   ONLINE       0     0     0
	  mirror-10  ONLINE       0     0     0
	    mfid10   ONLINE       0     0     0
	    mfid24   ONLINE       0     0     0
	logs
	  mirror-11  ONLINE       0     0     0
	    mfid13   ONLINE       0     0     0
	    mfid26   ONLINE       0     0     0
	cache
	  mfid12     ONLINE       0     0     0
	  mfid25     ONLINE       0     0     0
	spares
	  mfid11     AVAIL

errors: No known data errors

The logs show loads of mfi1 and mfid16 errors for a few minutes, and then
(presumably when ZFS dropped the disk) nothing relevant after that. ZFS
hasn't logged anything, not even that it's failed a disk.

I've manually done a 'zpool replace data mfid16 mfid11' which has brought
the spare in without problems, but I'm eager to learn what I did (or didn't
do?) to cause the spare to not be used automatically.

Thanks in advance,


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