Anyone interested in a storage server has probably looked into some form of RAID - namely those that dont waste half of your capacity as raid 1 or 0+1 does. This means Raid 3,4,5,6 etc. (although 6 is for REALLY high end crap..) Raid 5 has been usually touted as standard for servers and it's easier to see why now.
Maximum pc released their dream machine featuring as their harddrive controller, a Netcell Raid 3 sata controller -paper specs are nice - no drivrers needed, 128MB memory for cache, hadware xor for parity generation - but being raid 3, theory points to bad performance. This didnt stop a bunch of people from jumping on the raid 3 bandwagon.
raid 3 - one disk for parity, byte level writing.
raid 4 - one disk for parity, block level writing.
raid 5 - parity rotated on all disks, block level writing.
rotating the disk on parity wont affect performance, but here's how byte vs block compares
when you write, or read, you're doing this in segments, i.e. blocks. For a raid 3 array to read a file, each drive head MUST be aligned to read the current block it's on. if another file must be read from or written to at this point, all drive heads must align to that sector on each drive - the seek time being the time for the SLOWEST seek.
Now for raid 5, only one disk is reading each block - so time to read an individual block is longer - a long stream of contiguous blocks would be slower, but for random access, each seek remains the average seek for that disk. For multiple reads and writes, depending on the complexity of the controller, they can be handled simultaneously so long as the blocks reside on seperate disks.
it's unfortunate that this review didn't have a raid 5 array for comparison, though as 1+0 comes on most mobos nowadays, it's not bad to consider. the cost of these netcell-xfx raid 3 cards is low compared to high end cards - $230 for the 5 port sata card on newegg, and while it's bad for multiple readers/writers, it's not too bad for a small low performance file storage server with redundancy for safety.
http://techreport.com/reviews/2005q4/xfx-revo64/index.x?pg=1
