ZFS does support different sized drives, and you can add disks to a pool easily.<p>It does not support different sized drives in a raidz (equivalent to an mdadm array), as far as I know, but you can mix raidz and singular drives in a pool, though that is a bit silly. It also does not support adding disks to a raidz, which is equivalent to growing a raid5 or raid6 array, which is admittedly a pain in the ass.