Replying to @⁨ThePantser@sh.itjust.works⁩

How much data do you have, and are the drives identical? Usually I do in-place conversions by taking some drives offline, creating a degraded raid on them, migrating the data, then wiping the remaining drives and bringing them online in the new raid.

Works for zfs pools too, but you can’t create a pool with missing drives, you have to create a temporary block device then mark it offline, then replace it with the real drive once it’s free.