RAID 5 is useful everywhere else, especially if it is deployed with proper hot-swap chassis. These can even be set up with FreeBSD and Linux systems using a SCSI-SCSI RAID solution like the Mylex DAC960SI with a RISC CPU on board (http://www.mylex.com).
With a RAID 5 hot-swap scenario you do need to buy more drives though. All drives are the same capacity and ideally are the same model with consecutive sequence numbers although that isn't critical. One drive's worth of capacity (striped over all drives though) is used for the parity information that allows the system to CONTINUE operation even if any single drive fails. And you need an additional drive to sit there waiting as a hot spare. If there is no hot spare, performance will be slower and you will lose your safety margin (parity redundancy) until you physically remove and replace the dead drive. Since you are going to want to stock at least one spare it might as well be a hot one. If there is a hot spare, the RAID system automatically takes care of rebuilding the array on the fly without interrupting service and minimizes the window during which you have no safety margin.
Ideally, this array would have 1 parity drive, 1 hot swap spare, 1 additional shelf spare and then 4 or more data drives. IMHO 4 is the mnimum number of data drives you should use and 1 is the minimum number of spares you should have either hot or shelf. The drives should be about 2 gig drives or so. No bigger and no smaller unless you can find a batch of new 1 gig drives.
RAID is almost necessary for a full news feed today but don't stop there. If you expect to continue growing, plan for *WHEN* you will implement RAID 5 on all your servers, not *IF*. Some people may prefer the idea of an NFS toaster and this is not that bad of an idea, but I prefer the straight RAID 5 solution myself. Mainstream UNIXes like SCO and Solaris will all support RAID host adapters that plug into the bus. All UNIXes will support the SCSI-SCSI style of RAID controller that plugs into a high speed SCSI host adapter and handles all the drives on its own SCSI busses.
Hot swap chassis are available with many brand name server machines like IBM PC720, AST Manhattan, and others but only support mainstream OSes like SCO or perhaps Solaris. And if you use SUN boxes you have similar options. But there are some generic hot-swap chassis that will work with the SCSI-SCSI RAID solutions and the best way to find these is to ask the manufacturer of your RAID controller. In addition to Mylex, I understand DPT makes a SCSI-SCSI RAID and another company whose name begins with C but I can't remember.
Michael Dillon ISP & Internet Consulting Memra Software Inc. Fax: +1-604-546-3049 http://www.memra.com E-mail: michael@memra.com