I did not emphasize a very important aspect of my discussion of media storage expansion options: a critical aspect of setting up a software RAID array is the utility you use to set up the RAID, and SoftRAID is a better option than Apple’s Disk Utility.
SoftRAID allows you to set up a RAID 0 or RAID 1. I hope in a future version they will also support RAID 10, which Apple added to their Disk Utility in Tiger.
RAID 0 is striping data over multiple disks for improved performance, RAID 1 is mirroring data over multiple drives for improved realiability and RAID 10 (a.k.a. RAID 1+0) is a combination of striping and mirroring. There are many more RAID configurations, but many require hardware controllers. RAID 1 and 0 is easily implemented with software. I prefer SoftRAID rather that using the built-in OS X Disk Utility RAID feature because SoftRAID offers several advantages. Disk Utility provides a no-frills interface but you have to use the command line interface to rebuild in the event of the failure of a mirror disk, and a RAID configured with Disk Utility is less reliable becuase Apple does not offer error checking and reporting. SoftRAID, on the other hand, provides reports of volume status and the interface makes it easy to create and maintain RAID volumes. A list of differences is available.