Also write down the SCSI numbers or IDE names for each disk so you can put the system together again in the right order. For checking your hard disks you can use the Disk Advisor boot disk available on the net . The disk builder required Windows to run. This system is useful to diagnose failed disks. You are strongly recommended to make a rescue disk and test it.
Most distributions make on available and is often part of the installation disks.
For some, such as the one for Redhat 6.1 the way to invoke the disk as a rescue disk is to type linux rescue at the boot prompt. There are also specialised rescue disk distributions available on the net. When need for it comes you will need to know where your root and boot partitions reside which you need to write down and keep safe. A rescue disk is self contained and will work even if there are no hard disks. Create an account.