Zpool attach vs zpool replace

I have a NAS with a zpool that is made up of one mirrored vdev of 8TB HDDs. I’m replacing the drives with 2 new 16TB drives (for the increased space).

  • Is there a difference between running:
    • zpool replace the old drives with the new drives
    • zpool attach the new drives, waiting for it to resilver, and zpool detach of the old drives
  • Is there an preferred way to do two drives at once? I imagine that when it is resilvering both drives it would be more efficient to run them simultaneously instead of one a minute behind the other. That way its reading the data once and writing it twice instead of reading the data twice and writing it twice. But that’s purely conjecture.

Any suggestions? Thanks!