What are RAID hard disks? Should I go for SATA or SCSI?

RAID stands for Redundant Array of Inexpensive Disks and is the process of grouping multiple hard disks together so that Windows sees them as one hard disk (note that the hard disks, or at least the partitions used in the RAID, must be an identical size). This may be desirable to improve performance by writing half the data to one disk and half the data to the other disk at the same time (known as striping or RAID 0). Alternatively, RAID 1 (also known as mirroring) is used for fault tolerance, whereby all of the data is written to one hard disk and then again to a second hard disk so that you have an exact duplicate backup copy, though this gives slightly decreased performance. RAID 0 is not at all fault-tolerant – if one of the hard disks goes down, you’ll lose half of every file that has been saved, therefore corrupting ALL of your data.

RAID 5 (striping with parity) gives better performance by striping across 3 hard disks. Only one fifth of the total drive space is lost to parity data so the three hard disks used in RAID 5 can be smaller than the two hard disks used in RAID 0 in order to achieve the same amount of total storage space in Windows.

The next level up is RAID 10 and RAID 0+1, both of which are different ways of implementing striping AND mirroring - very fast and redundant but you need a minimum of 4 identical hard disks so it is a more expensive option.

With regard to the RAID, my choice of SATA or SCSI would depend on what I wanted the RAID for. Do you want it for performance, i.e. RAID 0 striping, or for redundancy, i.e. RAID 1 mirroring? For throughput of data, the fastest SCSI drives handle big data faster than the fastest SATA drives. Personally, I would prefer a SATA RAID in a home PC as it will be quieter and, if you go for one of the Western Digital ranges, for example, SATA disks offer server-class reliability on a par with SCSI drives. But cheaper.

The above information refers to the 5 most common RAID configurations but there are others. I recommend a visit to the simple yet comprehensive tutorials at www.RAID.com if you need more information.