I'm planning on doing a backup of a 2 disk mirror before doing an upgrade on the pool (an old maczfs pool, I posted about this recently in the non openzfs pools subforum.) I'm running 1.6.1.
The current mirror is two 4tb drives. I have a 3rd 4tb drive so I was thinking I could just attach it to the pool and wait for it to resilver, then remove it from the pool before upgrading. If the upgrade fails horribly I can use my new 3rd drive copy to immediately reconstruct the original rather than having to copy from other format backups (I have files on a western digital mycloud mirror which I'm not that happy with).
Anyway, the question is, what is the best way to do this, or is there something bad or flawed with this idea? I've found other zfs discussions online elsewhere about this and they suggested attaching and then splitting the new disk off. I was originally thinking of either attaching, resilvering and detaching or attaching a spare, resilvering and removing it. I would like input about the os x version rather than another fork...
Which of these would work or would be best?
After I get a successful pool upgrade (I will trust a scrub unless there is a better idea) I will reuse this disk in a new mirror.