Rich, We have a two tiered strategy for low cost serving. For IDE drives, we use an Intellimirror device. It's a hardware mirroring device that maintains two identical IDE drives. If one fails, the system runs on the other one.
Main downside is that it's slow.
Main upside is that it's cheap. For SCSI, we use dual controllers and dual hard disks - then set up software mirroring across the partitions. I've heard, but have not tested, that the mirrored partition is not bootable in the event of failure, so I'm only using the SCSI disks for data and programs, and keeping the OS on the IDE's. I put an IDE drive in to do disk to disk backup, and then upgraded the single drive to an Intellimirror as our capacity exceeded the SCSI drives. Moved everything over to the IDE drives, thus slowing it down, but saving myself from a catastrophy when one of the SCSI drives failed.