Alot have been said about RAID0. If the proper conditions, RAID0 can increase sequential throughput (MB/s) and I/O operations per second (IOps) when doing random-like I/O. I would say the IOps are the most important. But there's latency too, which becomes especially important with things like application-loading and booting, but also general system responsiveness.
RAID0 cannot lower the latency of your mechanical drives, but it can increase performance of desktop and server applications. Its a misconception that RAID0 only increases performance when handling "large files", the IOps story is more complicated and requires proper setup of your RAID.
For one, you need alignment. Windows XP and below align partitions improperly. So you need at least Vista/Win7, in Linux this is pretty straightforward too.
Then, you need a large enough stripesize, 128KiB or larger, to allow one I/O request to *only* be handled by one disk in the array, and not overlapping data on multiple disks. The idea behind this is that each disk can process a different I/O request at the same time, theoretically providing 100% scaling with the number of disks. But reads/writes may not be spread evenly to all disks, so this number is lower in reality when doing random I/O.
Story short, it can provide some additional performance if properly setup. However, given that SSDs can be thousands of times faster than HDDs when doing "difficult" random-like I/O, a good SSD could outperform many Velociraptors in RAID0.
That said, velociraptors do pack a reasonable 300GB of storage and are among the fastest of desktop-class HDDs.
I had 2 300mb Velocity Raptors in Raid 0 and was not impressed to say the least. I had excellent hardware - ASUS Rampage II Extreme X58 board, 6Gb OCZ 1866 Ram, Core 7 processer @ 3.7Ghz, etc.
I 1st used the the raid built into the board - wasn't as impressed as I would have liked to have been
2nd I connected them to an Areca raid controller & the performance improved a little.
I kept the 2 velocity raptor drives as my OS drives, and connected them back to the motherboards raid controller.
Purchased 2 Seagate Cheetah 15K.6 drives (300Gb 15k RPM SAS drives} don't know why, just did. I liked them a little bit more than the raptors. Until I tried 4- $120 hard drives I had sitting on my desk that i had to to install in a friends computer later.
He had 4 Seagate 1.5Tb drives sitting there. I had nothing to do in the next few minutes, so I set them up. Raid 0, then 5. I would have tried 6, but I was getting bored by that time. I realize the difference in the velocity raptor drive / the cheetah 15k6 / and the unreliable seagate 1.5tb. I know which drives are going to do better in which situation also, so don't comment back anything stupid.
The 4 1.5Tb seagate drives absolutely amazed me. I'm a computer administrator by day and just a regular person at night. At home as a home user, the transfer rates of these drives more than doubled the Seagate & nearly tripled the Raptors.
All that said, I wouldn't spend the money for the raptor drives, I would invest in 2-high end/enterprise 1Tb upto 2Tb drives instead. It's been my experience that the larger the drive the better the performance you get. (2) 2Tb drives in Raid 0 ahould scream.
A pair of velociraptors will beat a pair of 2tb drives any day. The sequential rates might be similar, but overall performance for an OS drive will be quite different. The access times of the velociraptors will be 6-7ms, while for the larger drives, it will be 15ms or longer (all 2TB drives on the market right now are <7200rpm). I've got a pair of velociraptors in my system, and I've compared them to fairly impressive RAID setups with 7200rpm drives, and the velociraptors are definitely snappier. You do pay more for them, but I think it's worth it.
So its like 240MB/s start and 160MB/s end, a very good performance. And you're right; the Velociraptor doesn't degrade much in speed, whereas with normal 7200rpm disks the speed of the end of the disk is about 45% lower performance than the start, so about half the performance. Looking at the velociraptor that seems to be closer to 25-30% which is a good performance.
Personally, i think this is due to the SCSI-way of building enterprise disks. The 74GB raptors had the same issue; they just sacrifice capacity to gain speed. So perhaps the velociraptor could have been 600GB but by making it a 300GB drive it will perform alot better and its a performance-targeted drive. It would also make seeks faster.
The velociraptor is about the best compromise you can get atm, for a traditional HDD its very fast. But my point was, that while people are looking at MB/s scores, in case of the HDD we have to remember these are "best case scenario". Where with the SSD, the speeds are something you would always get, even with fragmentation or location of the end of the disk.
So for HDD the STR is the "maximum STR" and not the average or lowest STR score they can put out. For SSD's, the sequential rates are a flat line, so they are pretty much guaranteed.