Update on 2015 Oct 15: Today I discovered the
zpool split command, which splits a new pool (with a new name) off of an existing pool.
split is much cleaner than
detach, as both pools can then exist (and be scrubbed separately) on the same system. The new pool can also be cleanly (and properly)
export[ed] prior to being unplugged from the system.
(My original post follows below.)
Warning! Various comments on this page imply that it is (or might be) possible to
zpool detach a drive, and then somehow reattach the drive and access the data it contains.
However, according to this thread (and my own experimentation)
zpool detach removes the "pool information" from the detached drive. In other words, a
detach is like a quick reformatting of the drive. After a
detach lots of data may still be on the drive, but it will be practically impossible to remount the drive and view the data as a usable filesystem.
Consequently, it appears to me that
detach is more destructive than
destroy, as I believe
zpool import can recover destroyed pools!
detach is not a
umount, nor a
zpool export, nor a
In my experimentation, if I first
zpool offline a device and then
zpool detach the same device, the rest of the pool forgets the device ever existed. However, because the device itself was
offline[d] before it was
detach[ed], the device itself is never notified of the
detach. Therefore, the device itself still has its pool information, and can be moved to another system and then
import[ed] (in a degraded state).
For added protection against
detach you can even physically unplug the device after the
offline command, yet prior to issuing the
I hope to use this
import process to back up my pool. Like the original poster, I plan on using four drives, two in a constant mirror, and two for monthly, rotating, off-site (and off-line) backups. I will verify each backup by importing and scrubbing it on a separate system, prior to transporting it off-site. Unlike the original poster, I do not mind rewriting the entire backup drive every month. In fact, I prefer complete rewrites so as to have fresh bits.