For all my servers in my environment I have redundant scsi cards and duplexed drives. If a controller or a hard drive fails it will switch over automatically. We use all the same or similar hardware. If a motherboard dies we have a spare machine waiting for us to pop our cards and drives into and we are back up shortly.
If you are using virtualization you can create the machines backups on standby and flip the switch when necessary. But personally I like having options. and Different setups for different environments. If you update this with a little more information on your setup I can give you a better answer.