RAID Tips 5 of 10 - Hot Spares

Hot spares are a good addition to a fault-tolerant array.

If a drive has failed in a fault-tolerant (RAID 1 or RAID 5) array, there is a vulnerability window. If another drive fails during this vulnerability window, the data is lost. Hot spare drives allow the controller to rebuild the array without administrator intervention, thereby reducing the vulnerability window.

The need for a hot spare increases as the number of disks in array increases.

Hot spares are most effective when a single hot spare drive is shared between several arrays. Consider for example an 8-bay NAS. If there is only one RAID 5 array in the NAS, then RAID 6 may be a better option than a hot spare. The hot spare drive just sits there idly. In a RAID 6 array, the same drive would be utilized to improve a read speed. However if you need two RAID 5 arrays, the hot spare drive is shared between these two arrays, reducing the disk space overhead.


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