Q: How do I calculate the available space on three different sizes of RAID 5 disks? A: First off, I wouldn't recommend building a RAID 5 group on dissimilar disk drives. All drives should have the same speeds and capacities. Unless you have a special type of adapter, RAID 5 requires capacity across drives to be the same. When you mix drive sizes, the drive with the smallest capacity is the total usable space per drive. So in a RAID 5 set comprising 60GB, 80GB and 40GB drives, the most you can get is 2 x 40GB. That's 80GB, with the third 40GB going to parity. All remaining space (60GB) is wasted and totally inaccessible. I recommend acquiring three drives of the same size to set up a RAID 5. The result for three 80GB drives would be 2 x 80GB or 160GB, with 80GB going to parity. Regardless of the number of drives in the set, one drive's worth of space is always lost to parity in a RAID 5 configuration. --Ashley D'Costa, enterprise solutions architect, Mainland Information Systems