Additionally, the RAID subsystem should support an on-line spare, which allows for a spare drive to replace a failed drive automatically and hot swapping capability, which allows for the removal of any drive without having to shut down the system. Disk fault tolerance is essential in any server environment besides backups. Some people mistakenly eliminate total system backups, thinking that a fault tolerant disk subsystem is enough protection. A RAID system doesn't reduce the chance of total system failure due to a natural disaster, accidental file deletions or theft. Also consider storing the backups either in a different location in your facility or, better yet, offsite.
Systems employ other features, such as redundant CPUs.
NetFrame uses a technology called Gemini mode, which enables two CPUs to execute instructions in lockstep mode. If one processor detects an error with the other CPU, that CPU is disabled. Other facilities that help maintain maximum availability are remote server monitoring and management. This allows the server to send alerts to a central management console. Consider technical support, servicing and the availability of replacement parts.