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Date: Thu, 29 Aug 2013 10:27:28 +0200
From: Maurizio Vairani <maurizio.vairani@cloverinformatica.it>
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Subject: Boot problem if a ZFS log device is missing
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Hi all,
I am using an USB memory stick as cache and log devices for a HDD ZFS 
pool named tank0:
$ zpool status -v tank0
   pool: tank0
  state: ONLINE
   scan: scrub repaired 0 in 7h19m with 0 errors on Tue Jul 30 06:11:23 2013
config:

     NAME         STATE     READ WRITE CKSUM
     tank0        ONLINE       0     0     0
       ada0s1d    ONLINE       0     0     0
     logs
       gpt/SLOG   ONLINE       0     0     0
     cache
       gpt/L2ARC  ONLINE       0     0     0

errors: No known data errors

If I remove the stick before booting the laptop (a Compaq Presario) it 
will not boot with the error message:
"Mounting from zfs:tank0 failed with error 6"
end the mountroot> prompt is displayed.
I need to reinsert the stick to completing the boot process before 
restarting the laptop.

It is possible to boots the laptop without stick if I remove the log 
device with the command:
# zpool remove tank0 gpt/SLOG
before switching it off. The pool will works in degraded mode because 
the cache device is missing, but it works.

I am able to boot the PC without a cache device but not without a log 
device. Why ?
The laptop is updated to 9.2-PRERELEASE r254783.

Regards
Maurizio