Originally posted by: Tizyler
Yeah, I plan on doing RAID 0. So if I have a regular 7200 RPM drive paired up with a Raptor, would I just be slowing down the raptor--as opposed to speeding up the couple?
Yes, of course the speed of the slower drive will bring down the speed of the composite compared to two Raptors.
There are roughly two different ways of configuring RAID 0.
(1) The most commonly used on is with 64k stripe size. This is also the most common file access unit. So if the OS requests one 64k block, then another, it would go to one drive and the other, alternating among the two. This would in theory be as slow as a single drive access, and in this case, slower than a single Raptor access.
(2) Another stripe size would be 64k / number of drives. In this case, a 64k block request would have to be split among both drives, and the request would be satisfied when the slowest drive responded. So this would be like a stripe of two slow drives, and the Raptor's higher performance wouldn't help. The composite should be faster than one Raptor, but only if two of the slow drives used in this way are faster than one Raptor.
Reality can be more complicated with read-ahead, etc., and so even with case (1), both drives could be run in parallel to some degree, and the composite would be faster than just one Raptor. The composite may be just as fast as two 7200's, just as in case (2).
Another factor which applies here is that usually more than the raw transfer rate matters (i.e. access time dominates sometimes), and here the RAID may either bring down the composite to the slowest of the two, or to the average of the two -- slower than one Raptor.
RAID also brings with it added complexity of setup, management, portability, and additional risk due to RAID itself and due to higher numbers of drives sharing the same data.
In many cases performance can be improved by splitting data manually across two drives -- e.g. OS + swap + user folders on one drive, and programs + data on the other. Here access to the two drives would be naturally concurrent in some cases. Setup, maintenance and portability would be simpler, and the risk would be lower.
