japes wrote:zfs send | zfs receive is what you're looking for. They may have renamed it, but that should help your google-fu.
+1 to that. If this is a boot disk you need to reinstall grub to it though. The other alternative is to 'attach' the disk as a mirror, let it silver up, then remove the smaller disk. It should grow to the rest of the disk when smaller disk removed. In either case, if this is rpool you still need to install grub.