So you break down the server and services into components and put them in a graph or excel sheet.
This will help to make sure your not "over engineering" the system. Disks can use different raid systems to give redundancy.
Have your network backup occur on a different ethernet device.
Every time a computer is turned on, as part of the boot process the BIOS tries to find a bootable drive to continue the loading process by starting its first sector.
However, if BIOS is unable to find a drive to boot from, then a “Disk Boot Failure” error screen is displayed and the boot process is halted.
Remember, redundancy always comes with a dollar amount cost.
And this dollar amount will determine your range of options to implement redundant technologies or processes.
From the Single Node Cluster Installation Guide - Rev 1 June 2008: Note: Red Hat Cluster Suite consists of Red Hat Cluster Manager and Linux Virtual Server Cluster. In this guide, Red Hat Cluster Suite refers only to Cluster Manager.