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Add a mirror with ZPOOL/ZFS

Recently I had a huge debacle involving a USS7110, which happens to be a Sun x4240 with ZFS, moderately over-glorified ;-)

As a result of the disaster I was essentially pulling the mirror disk from my alternate system (uss02) and putting it into my primary system (uss01) to get that system running again. Simple enough... I guess. The problem I ran into, and this will be specific to the USS only, is that the drives in the array are either identified as "system" or "data" (which you can see from the BUI). During my drive swapping, I had pulled the "data" spare, and mirrored the "system" OS disk to it. Somehow it left the data disk-type stamp on it. The drive mirrored fine and all, but when I would go to create a new zpool, the OS drive would appear to be a valid disk to put the data on. I obviously didn't go through with that step, but I can't imagine what would happen if I had.

Chances are you will never be in the position I was in, so the details hardly matter. The crux of this post is how to add a mirror to an existing ZPOOL.

  • You will notice that my "system" zpool only has one disk.
  • I had to use -f because the disk I was about to mirror to had previously belonged to another pool. I suppose you could reformat that drive before going through with this activity, but... the drive has the SATA WWN on the label, so I was certain I had the correct device
  • Why am I posting something so trivial/simple... the syntax seemed odd to me and therefore I wanted a reference to successfully pulling this off. See the very bottom for an explanation.
uss02# zpool status
pool: system
state: ONLINE
status: The pool is formatted using an older on-disk format. The pool can
still be used, but some features are unavailable.
action: Upgrade the pool using 'zpool upgrade'. Once this is done, the
pool will no longer be accessible on older software versions.
scrub: none requested
config:

NAME STATE READ WRITE CKSUM
system ONLINE 0 0 0
c0t5000CCA0002CE1C4d0s0 ONLINE 0 0 0

errors: No known data errors

uss02# zpool attach -f system c0t5000CCA0002CE1C4d0s0 c0t5000CCA0002D2844d0s0
uss02# zpool status system
pool: system
state: ONLINE
status: One or more devices is currently being resilvered. The pool will
continue to function, possibly in a degraded state.
action: Wait for the resilver to complete.
scrub: resilver in progress for 0h0m, 0.02% done, 8h10m to go
config:

NAME STATE READ WRITE CKSUM
system ONLINE 0 0 0
mirror-0 ONLINE 0 0 0
c0t5000CCA0002CE1C4d0s0 ONLINE 0 0 0
c0t5000CCA000D2844d0s0 ONLINE 0 0 0 7.07M resilvered

errors: No known data errors


Explanation:
zpool attach [-f] pool device new_device

Attaches new_device to an existing zpool device. The
existing device cannot be part of a raidz configuration.
If device is not currently part of a mirrored configura-
tion, device automatically transforms into a two-way
mirror of device and new_device. If device is part of a
two-way mirror, attaching new_device creates a three-way
mirror, and so on. In either case, new_device begins to
resilver immediately.

-f

Forces use of new_device, even if its appears to be
in use. Not all devices can be overridden in this
manner.

So - when I see (device) (new-device) I generally think of (replacing) a device, not mirroring. This is totally my issue, of course. Perhaps a better syntax would be (source) (target) or something.
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