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List:       zfs-discuss
Subject:    [zfs-discuss] Can't offline second disk in a mirror
From:       Boyd Adamson <boyd-adamson () usa ! net>
Date:       2008-01-31 2:43:35
Message-ID: 1619191A-3CE6-4169-A3D2-A8FFBA6D194D () usa ! net
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Since I spend a lot of time going from machine to machine so I thought  
I'd carry a pool with me on a couple of USB keys. It all works fine  
but it's slow, so I thought I'd attach a file vdev to the pool and  
then offline the USB devices for speed, then undo when I want to take  
the keys with me. Unfortunately, it seems that once I've offlined one  
device, the mirror is marked as degraded and then I'm not allows to  
take the other USB key offline:

# zpool create usb mirror /dev/dsk/c5t0d0p0 /dev/dsk/c6t0d0p0
# mkfile 2g /file
# zpool attach usb c6t0d0p0 /file
# zpool status
    pool: usb
  state: ONLINE
  scrub: resilver completed with 0 errors on Thu Jan 31 13:24:22 2008
config:

         NAME          STATE     READ WRITE CKSUM
         usb           ONLINE       0     0     0
           mirror      ONLINE       0     0     0
             c5t0d0p0  ONLINE       0     0     0
             c6t0d0p0  ONLINE       0     0     0
             /file     ONLINE       0     0     0

errors: No known data errors
# zpool offline usb c5t0d0p0
Bringing device c5t0d0p0 offline
# zpool status
   pool: usb
  state: DEGRADED
status: One or more devices has been taken offline by the administrator.
         Sufficient replicas exist for the pool to continue  
functioning in a
         degraded state.
action: Online the device using 'zpool online' or replace the device  
with
         'zpool replace'.
  scrub: resilver completed with 0 errors on Thu Jan 31 13:24:22 2008
config:

         NAME          STATE     READ WRITE CKSUM
         usb           DEGRADED     0     0     0
           mirror      DEGRADED     0     0     0
             c5t0d0p0  OFFLINE      0     0     0
             c6t0d0p0  ONLINE       0     0     0
             /file     ONLINE       0     0     0

errors: No known data errors
# zpool offline usb c6t0d0p0
cannot offline c6t0d0p0: no valid replicas
# cat /etc/release
                         Solaris 10 8/07 s10x_u4wos_12b X86
            Copyright 2007 Sun Microsystems, Inc.  All Rights Reserved.
                         Use is subject to license terms.
                             Assembled 16 August 2007


I've experimented with other configurations (not just keys and files,  
but slices as well) and found the same thing - once one device in a  
mirror is offline I can't offline any others, even though there are  
other (sometimes multiple) copies left.

Of course, I can detach the device, but I was hoping to avoid a full  
resilver when I reattach.

Is this the expected behaviour? Am I missing something that would mean  
that what I'm trying to do is a bad idea?

Boyd
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