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