It's not the number of disks involved in the RAID per say. It's the way the files are divided.
Think of it this way.
In RAID 1, you have two drives. Each drive has its own full file. Each disk is separate and self-contained. You lose one drive, no big deal, you still have the whole file on the second drive.
In Raid 0, you have two or more drives, but a single file is split (or striped) into the multiple drives (we'll say 2). So half the file is on one drive and the other half is on the other drive. Which means you still only have 1 file with a pointer between the two halves telling SQL Server where the rest of the data is. When SQL Server searches the striped data file, it starts at one point and moves through the file (regardless of what disk the current section is) in a logical and orderly manner. It does not search all sections of the striped file simultaneously because it's following the pointers. (Someone correct me if I'm wrong about this).
Raid 1+0 is a combination of the above two RAID methods.
Raid 5 is three or more disks with the file split (or striped) on all the drives. You still have only one file total and each drive contains a little bit of parity/checksum stuff for redundancy.
The key here is, even if you have multiple files in a RAID 5 or RAID 1+0, they will all be on the same sets of drives. Since each disk only has (usually) one controller, you can't search multiple files at the same time. The controller will only search for your data one file at a time then go onto the next file. It's terribly inefficient.
Now if you have multiple RAID 5 sets and stick a file on each different set, that's a different story. But this particular hardware config is not something I've seen IRL and you'd have to be pretty rich to afford a different RAID 5 / RAID 1+0 setup for each data file.
Does that help?
Brandie Tarvin, MCITP Database AdministratorLiveJournal Blog: http://brandietarvin.livejournal.com/[/url]On LinkedIn!, Google+, and Twitter.Freelance Writer: ShadowrunLatchkeys: Nevermore, Latchkeys: The Bootleg War, and Latchkeys: Roscoes in the Night are now available on Nook and Kindle.