I'm running in a RAID 1 config, which basically means I have two hard drives, and when one hard drive is being written to, the other gets written to also, creating a mirror image. If one drive ever failed, I'd be safe, with one drive still up.
This actually happened a week ago.
I was running 2x 320GB drives and one of them failed. Since I couldn't find an exact duplicate of the drive I was running, I opted for 2x 500GB's instead.
I thought the copying process would be intensive, but it wasn't.
I downloaded a free program called 'Seagate Diskwizard'. I have no reasons to think it wouldn't work with other makes of drive also, but I'm not sure:
It made the copying process as easy as can be, and copied over the 320GB bootable drive, to the 500GB drive, making that bootable too. Everything was mirrored over.
The difference was, I had more space on the two partitions I had created.