Which RAID level supports fault tolerance with parity written to only one drive?

The correct choice is RAID 5, which is a storage technology that provides fault tolerance through the use of parity. In RAID 5, data is striped across multiple drives along with distributed parity information, allowing for the recovery of data in the event of a single drive failure. The parity is calculated and written in such a way that it only requires the use of one additional drive alongside the data drives. This design enhances efficiency by spreading the parity data across all the included drives, allowing for better performance and storage utilization.

In contrast, RAID 3, while it also uses parity for fault tolerance, stripes data across multiple disks but writes the parity to a dedicated drive, which can create a bottleneck and limit performance in some scenarios. RAID 6 provides a higher level of fault tolerance by storing two sets of parity, allowing for the survival of two simultaneous drive failures, which inherently means it needs more storage overhead. RAID 10, a combination of mirroring and striping, does not use parity at all but rather duplicates data across drives for redundancy.

The design of RAID 5 allows it to effectively balance performance, storage efficiency, and fault tolerance, making it a widely used configuration for balancing these factors in various server environments.