zpool scrub on pool from geli devices offlines the pool?

[Nikolay Denev]

Hi,

I have a zfs pool from 24 disks encrypted with geli.

I just did a zpool scrub tank, and that probably reopened all of the devices, but this caused geli "detach on last close" to kick in 
which resulted in offline pool from UNAVAILABLE devices. 

  pool: tank
 state: UNAVAIL
status: One or more devices are faulted in response to IO failures.
action: Make sure the affected devices are connected, then run 'zpool clear'.
   see: http://illumos.org/msg/ZFS-8000-HC
  scan: scrub in progress since Thu Oct  4 21:19:15 2012
        1 scanned out of 8.29T at 1/s, (scan is slow, no estimated time)
        0 repaired, 0.00% done
config:

	NAME                      STATE     READ WRITE CKSUM
	tank                      UNAVAIL      0     0     0
	  raidz2-0                UNAVAIL      0     0     0
	    4340223731536330140   UNAVAIL      0     0     0  was /dev/mfid1.eli
	    5260313034754791769   UNAVAIL      0     0     0  was /dev/mfid2.eli
	    3388275563832205054   UNAVAIL      0     0     0  was /dev/mfid3.eli
	    4279885200356306835   UNAVAIL      0     0     0  was /dev/mfid4.eli
	    17520568003934998783  UNAVAIL      0     0     0  was /dev/mfid5.eli
	    14683427064986614232  UNAVAIL      0     0     0  was /dev/mfid6.eli
	    5604251825626821      UNAVAIL      0     0     0  was /dev/mfid7.eli
	    2878395114688866721   UNAVAIL      0     0     0  was /dev/mfid8.eli
	  raidz2-1                UNAVAIL      0     0     0
	    1560240233906009318   UNAVAIL      0     0     0  was /dev/mfid9.eli
	    17390515268955717943  UNAVAIL      0     0     0  was /dev/mfid10.eli
	    16346219034888442254  UNAVAIL      0     0     0  was /dev/mfid11.eli
	    16181936453927970171  UNAVAIL      0     0     0  was /dev/mfid12.eli
	    13672668419715232053  UNAVAIL      0     0     0  was /dev/mfid13.eli
	    8576569675278017750   UNAVAIL      0     0     0  was /dev/mfid14.eli
	    7122599902867613575   UNAVAIL      0     0     0  was /dev/mfid15.eli
	    6165832151020850637   UNAVAIL      0     0     0  was /dev/mfid16.eli
	  raidz2-2                UNAVAIL      0     0     0
	    2529143736541278973   UNAVAIL      0     0     0  was /dev/mfid17.eli
	    5815783978070201610   UNAVAIL      0     0     0  was /dev/mfid18.eli
	    10521963168174464672  UNAVAIL      0     0     0  was /dev/mfid19.eli
	    17880694802593963336  UNAVAIL      0     0     0  was /dev/mfid20.eli
	    2868521416175385324   UNAVAIL      0     0     0  was /dev/mfid21.eli
	    16369604825508697024  UNAVAIL      0     0     0  was /dev/mfid22.eli
	    10849928960759331453  UNAVAIL      0     0     0  was /dev/mfid23.eli
	    7128010358193490217   UNAVAIL      0     0     0  was /dev/mfid24.eli

errors: 1 data errors, use '-v' for a list

Dmesg shows :

GEOM_ELI: Detached mfid1.eli on last close.
…
GEOM_ELI: Detached mfid24.eli on last close.

I then did /etc/rc.d/geli restart and zpool clear tank, and it is back online, but shows permanent metadata errors…

Any ideas why this happned from a simple zpool scrub, and how it can be prevented?
Just disable "detach on last close" for the geli devices?