RAID 1 would mirror two drives. RAID 5 requires 4 drives. Raid 5 will give you read speeds close to Raid 0.
For RAID 1: Increased read performance occurs when using a multi-threaded operating system that supports split seeks, very small performance reduction when writing. Array continues to operate so long as at least one drive is functioning.**
Ford RAID 5: Distributed parity requires all drives but one to be present to operate; drive failure requires replacement, but the array is not destroyed by a single drive failure. Upon drive failure, any subsequent reads can be calculated from the distributed parity such that the drive failure is masked from the end user. The array will have data loss in the event of a second drive failure and is vulnerable until the data that was on the failed drive is rebuilt onto a replacement drive.**
You can build an array with non-identical drives, however the array will assume the capacity and performance of the smallest and slowest drive. I.E a 80gb 5400 RPM and a 250gb 7200 RPM will be seen as 80gb and access times will suffer. No buddy does this really, unless the drives are fairly similar. Not sure if it causes problems. There is JBOD (Just a bunch of Drives) which can combine drives of different sizes to be seen as one drive as a combined capacity but provides no redundancy.
Or you could do a Nested RAID 0+1 etc:
When nesting RAID levels, a RAID type that provides redundancy is typically combined with RAID 0 to boost performance. With these configurations it is preferable to have RAID 0 on top and the redundant array at the bottom, because fewer disks then need to be regenerated when a disk fails. (Thus, RAID 1+0 is preferable to RAID 0+1 but the administrative advantages of "splitting the mirror" of RAID 1 would be lost. It should be noted, however, that the on disk layout of blocks for RAID 1+0 and RAID 0+1 setups are identical so these limitations are purely in the software).**
**Wikipedia
Personally, I use RAID 0 in my current setup for several reasons. When I originally built my current system I bought the hard drives at different times. I originally had 1 250gb Maxtor and almost a year later added an identical drive (was discontinued but got it open box cheap). I took the risk of data loss, but for important data I always had several back ups on DVD or on my web server. Currently I still have my RAID 0 array on the same drives but have added a single 500 Seagate as another backup option. I'm also experimenting using FreeNAS on my old box as a file server.
I recently did a HDtach on my Raid drives and my lone Seagate drive. I get about 105-107Mbps burst read (I think? or was it write, whichever) on my 2x250gb Maxtors and about 75Mbps on the Seagate. Access times were 14ms on the Maxtors and 12 on the Seagate. The Maxtors (alone) don't spec as high as the Seagate in access times and cache. Same RPM.
Raid does suck when you want to re/install Windows (XP yes, Vista?) as you'll need that ancient floppy drive to load the drivers for RAID.
***Also, I'm no where an expert on RAID and know the basics beyond 0/1. I'm sure there are there posters here that can fill in or correct me.
