everlasting log device

[Volodymyr Kostyrko]

Hi all.

When I get my hands on SSD device I tried to setup a log/cache partition 
for my pools. Everything works fine until one day I realized that I have 
a better place to stick this SSD in. I have upgraded system from 
RELENG_8_2 to RELENG_8 and tried to remove devices. From my two pools 
one was successfully freed from log/cache devices yet another one 
refuses to live without log device:

# zpool upgrade
This system is currently running ZFS pool version 28.

All pools are formatted using this version.

# zfs upgrade
This system is currently running ZFS filesystem version 5.

All filesystems are formatted with the current version.

# zpool status
   pool: utwig
  state: DEGRADED
status: One or more devices could not be opened.  Sufficient replicas 
exist for
         the pool to continue functioning in a degraded state.
action: Attach the missing device and online it using 'zpool online'.
    see: http://www.sun.com/msg/ZFS-8000-2Q
  scan: resilvered 0 in 0h21m with 0 errors on Sat Jul  2 15:07:35 2011
config:

         NAME                                            STATE     READ 
WRITE CKSUM
         utwig                                           DEGRADED     0 
     0     0
           mirror-0                                      ONLINE       0 
     0     0
             gptid/ecb17af1-9119-11df-bb0b-00304f4e6d80  ONLINE       0 
     0     0
             gptid/03aed1f5-95a3-11df-bb0b-00304f4e6d80  ONLINE       0 
     0     0
         logs
           gptid/231b9002-a4a5-11e0-a114-3f386a87752c    UNAVAIL      0 
     0     0  cannot open

errors: No known data errors

   pool: utwig-sas
  state: ONLINE
  scan: none requested
config:

         NAME        STATE     READ WRITE CKSUM
         utwig-sas   ONLINE       0     0     0
           mirror-0  ONLINE       0     0     0
             aacd1   ONLINE       0     0     0
             aacd2   ONLINE       0     0     0

errors: No known data errors

# zpool remove utwig gptid/231b9002-a4a5-11e0-a114-3f386a87752c && echo good
good

And nothing changes - system needs that partition.

One more weird thing.

# zpool iostat -v utwig
                                            capacity     operations 
bandwidth
pool                                    alloc   free   read  write 
read  write
--------------------------------------  -----  -----  -----  ----- 
-----  -----
utwig                                    284G   172G     41     70 
272K   793K
   mirror                                 284G   172G     41     70 
272K   793K
     gptid/ecb17af1-9119-11df-bb0b-00304f4e6d80      -      -      8 
  27   456K   794K
     gptid/03aed1f5-95a3-11df-bb0b-00304f4e6d80      -      -      8 
  27   459K   794K
   gptid/231b9002-a4a5-11e0-a114-3f386a87752c   148K  3,97G      0 
0      0      0
--------------------------------------  -----  -----  -----  ----- 
-----  -----

System claims that this log device has 148K data. Is this the size of 
unwritten data? The number is still the same when booting into single 
user mode and doesn't change at all.

Can I remove this log device? Should I recreate the pool to get rid of 
this behavior?

-- 
Sphinx of black quartz judge my vow.