I'm wondering if ZFS can handle the following. Say I have FreeBSD installed on a zpool with two physical 500GB disks in a mirrored setup. These form the root partition, so only a maximum of 20GB is actually being used.
I would later want to replace the physical disks with two small SSDs in a mirrored setup. Is there a way to do this online? My idea was to add these disks to the zpool as extra mirrors, wait for resilvering to finish and then remove the old drives. Problem is that these new disks would be smaller than the originals.
An idea that I had is to just partition the 500GB drives, so that ZFS only gets, say, 30GB of space on each physical disk the rest being wasted. This way the SSDs would have more space, so I would not arrive at a shrinkage problem. Problem is that this way I need to estimate in advance the size of the future replacement disks. Is there a way to avoid this?