What is the significance of a spare disk in a disk shelf?

• A. A spare disk automatically replaces a failed disk in its RAID group to maintain redundancy.
• B. A spare disk is used for temporary storage during maintenance.
• C. A spare disk increases random access performance only.
• D. A spare disk stores logs of future failures.

Answer: (A)

A spare disk in a disk shelf acts as a hot spare, ready to take over automatically when a member of its RAID group fails. When a drive fails, the controller rebuilds the lost data onto the spare, preserving the RAID’s redundancy and keeping protection online without waiting for manual replacement. This reduces downtime and the risk of data loss because the array remains resilient during the rebuild. It isn’t used for temporary storage during maintenance, it doesn’t inherently boost random I/O performance, and it doesn’t store logs of future failures.