Add a new drive (sdf) to 4 disk raid array md0:- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ fdisk the new disk and make a partition of type fd (Linux raid autodetect) then add and grow the array: mdadm --add /dev/md0 /dev/sdf1 mdadm --grow /dev/md0 --raid-devices=5 The filesystem the needs to be expanded to fill up the new space. cat /proc/mdstat to find the new block count, eg 29302876116 blocks level 5, 64k chunk, algorithm 2 [5/5] [UUUUU] fsck.ext3 /dev/md0 resize2fs /dev/md0 29302876116 Credits: Ferg (http://scotgate.org/?p=107)