Synonymous with hot standby. See hot standby.
An extra disk drive in a RAID configuration that is ready and waiting to be put into action automatically when another drive fails. Using the RAID algorithms, the missing data from the faulty drive is reconstructed and written to the hot spare. When the bad drive is replaced, it then becomes the hot spare. If a hot spare is not used, then the faulty drive must be manually removed and replaced with a new one. See RAID and hot swap.