I have a fairly simple ZFS setup: one zpool, two mirror VDEVs, each consisting of two 4 TB WD Red drives. I have purchased four new WD Gold 14 TB drives. My question is, how best to add these drives to my zpool. I have thought of two options:
(1) create two new mirror VDEVs, each with two of the 14 TB drives. Effective storage would be ~8 TB from the existing VDEVs and ~28 TB from the two new VDEVs
(2) create one new mirror VDEV using two of the 14 TB drives. Save the other two new drives for building a second ZFS server as a remote backup target. Effective storage: ~8 TB from the existing VDEVs plus 14 TB from the new VDEV.
How should I be thinking about this? What are the criteria for designing an optimal setup?