A drive for a RAID 1 array fails.

A RAID 1 array uses disk mirroring, meaning all data is written identically to two drives. When one drive fails, the other contains a complete, current copy of the data. CompTIA A+ emphasizes that RAID 1 is designed for fault tolerance, allowing continued operation even after a disk failure.

The correct action is to replace the defective drive and allow the RAID controller to rebuild (sync) the mirror onto the new disk. This restores redundancy and ensures ongoing data protection. The system can typically continue running during the rebuild process.

Option A is incorrect because attempting to repair a failed drive is unreliable and unnecessary—RAID 1 already provides a healthy copy. Option B ignores the importance of restoring redundancy, leaving the system vulnerable to data loss if the remaining drive fails. Option D (restore from backup) is unnecessary because RAID 1 already preserves the data.

Therefore, the best solution is to install a new drive and resynchronize the array, preserving all data with minimal disruption.