I think given the 36GB drives, your only option is to do either a 5 drive RAID with a hot spare or a 6 drive RAID with a hot swappable, which would give approximately 170 to 180GBs of drive space.

Your other possibility is a RAID10, which will give you very good redundancy at the expense of space leaving you about 108GBs of space.

Bert
Pediatrics
Brewer, Maine