By adding the spare hard drive functionality to a RAID system, the resilience of the system is further increased in the event of a hard drive failure. The spare hard drive is an additional hard drive that is ready to take over immediately in case of a failure of another hard drive in the RAID.
Let's take the example of a RAID 5 with a defective hard drive. In a normal configuration without a spare hard drive, if a second hard drive were to malfunction as well, it would result in the complete loss of the RAID 5. All the stored data would then be unrecoverable. However, by using a spare hard drive, this situation can be avoided.
When a faulty hard drive is detected, the spare hard drive automatically and immediately takes its place. The data that was originally stored on the failed hard drive is then rebuilt on the new spare hard drive. This reconstruction helps limit the period during which the RAID operates in degraded mode, meaning with fewer operational hard drives.
It is important to note that the spare hard drive is never used unless there is a failure in the RAID system. It remains on standby, ready to be activated when needed. This ensures that the spare hard drive maintains its integrity and immediate replacement capability when a failure occurs.
Different RAID levels support the use of spare hard drives. These include RAID 1 + Spare, RAID 5 + Spare, RAID 6 + Spare, and RAID 10 + Spare. In all these cases, the spare hard drive is used to maintain the redundancy and resilience of the RAID system in the event of a hard drive failure.
In summary, the incorporation of a spare hard drive in a RAID system enhances fault tolerance and improves data availability. It is an essential preventive measure to minimize downtime and protect important data from potential losses.
Only the following RAID systems can handle a spare drive :