Which RAID configuration requires only one additional disk for redundancy and provides fault tolerance?

RAID 1 is the configuration that requires only one additional disk for redundancy and provides fault tolerance. In RAID 1, data is mirrored across two drives, so that if one drive fails, the other drive still contains an exact copy of the data. This setup not only offers fault tolerance but also allows for quick recovery since the data on the remaining operational drive is immediately accessible.

While RAID 5 does provide fault tolerance and uses striping with parity to allow for data recovery with one failed disk, it requires a minimum of three disks to operate. RAID 0, on the other hand, does not provide any redundancy—its purpose is to enhance performance by striping data across multiple disks without any fault tolerance. RAID 10, which combines RAIDs 1 and 0, requires at least four disks and provides redundancy and performance benefits but exceeds the requirement of just needing one additional disk for redundancy.

Hence, RAID 1 is the configuration that meets the criteria of needing only one additional disk while ensuring data protection through redundancy.