When this project was started (early 2002), the largest hard drive to be had was the Maxtor D540X with 160 GB. Its rotational frequency of 5,400 rpm is more than sufficient for RAID purposes and, what's more, keeps the system from overheating.

Each system (node) has three 3Ware controllers, each of which controls eight hard drives.

The complete backup system holds a total of 24 of these nodes in five large 19" cabinets. 24 hard drives times 24 nodes gives us an impressive total of 576 hard drives, each with 160 GB capacity. That puts the theoretical gross capacity at some 92,160 GB. From that, we have to deduct 11,520 GB to account for the fact that each RAID controller has one hot-spare drive. The arrays being used are RAID 5, which, all told, take up roughly the same capacity as a hard drive used to administer the parity data (unlike RAID 3, though, the parity data is spread among all the hard drives). So we have to deduct the same amount again from the gross capacity. That results in a net storage capacity of 69,120 GB.