The beauty of that being that when all the drives
have been retired/failed and the smallest partition
size is now 500GB or whatever you can
--grow=max and get that unused space.

Thanks. That's a good idea, because I would eventually like to make
the array larger than it is as the drives get replaced, one at a time.
Would the command be:
$ mdadm --grow /dev/md0 --size=max DEVICE1 DEVICE2 DEVICE3 DEVICE4

Felipe