Comments on Updating a ZFS Mirror

Comment by Freddie Cash

Wed, 04 Jan 2012 15:51:49 -0800

Just a note: you don't need to use zpool replace on mirror vdevs. Instead, just zpool detach the degraded disk from the vdev (thus turning it into a single disk vdev). And zpool attach the new disk to the remaining disk (thus turning it back into a mirror vdev).

zpool replace is only needed for raidz vdevs.

Comment by Romain Tartière

Thu, 05 Jan 2012 11:38:24 +0100

You are right: there is no need to zpool replace in this case. In fact, the man page indicates that this command does what you say in a single step (the only difference is the order of operations, and it's not critical):

zpool replace [-f] pool old_device [new_device] Replaces old_device with new_device. This is equivalent to attach- ing new_device, waiting for it to resilver, and then detaching old_device.

Let's face it: I am a lazy sysadmin ;-)

Comment by Firesock Serwalek

Sun, 05 Aug 2012 20:06:40 +0100

There may actually be an advantage to doing the replace method (and the order) over detach/attach. When you detach, certain details are removed from the disk, so if something goes wrong during the resilver, you can't just attempt to pop it back in. Presumably this is the reason behind the ordering of operations as well.

More details here:
http://www.mail-archive.com/zfs-discuss@opensolaris.org/msg15620.html