ZFS Drive swap

I built a ZFS 2 disk mirror on a Poweredge 2950 III server about a year ago using a couple Toshiba 2TB drives. Both drives are the same model but sourced from two different local Staples stores, but I'd still bet they are the same batch. I'm going to add another 2 disk mirror vdev to expand the pool and I'm considering swapping one of the original disks.

Does this make sense so that my existing zpool is one Toshiba and one Hitachi drive reduce the likelihood of both disks failing at the same time? I do have backups, but to minimize downtime does it make sense to add a spare, swap a new disk in and resolved, and then use the old disk and a new disk for the second vdev?

Attach a new disk to the existing 2-disk mirror, turning it into a 3-disk mirror vdev. Once the resilver is done, detach one of the original drives, dropping it back to a 2-disk mirror.

Then you can use that disk and a new disk to create a new 2-way mirror vdev, and add that to the pool.

Read through the zfs(8) man page for more information on attach/detach. You really don't want to use zfs replace on mirror vdevs (unless you have no extra physical ports/bays, of course).