RAID 6 extends the parity-based protection concept of RAID 5 by calculating and distributing two independent sets of parity data across the disk group instead of one, which specifically allows the array to reconstruct all data even if two drives fail at the same time, before either failed drive has been replaced and rebuilt. This dual-parity design is the defining characteristic that makes RAID 6 the correct choice whenever protection against two simultaneous disk failures is a stated requirement, which is particularly valuable in larger arrays with bigger drives, since rebuild times are longer and the statistical risk of a second failure occurring during that extended rebuild window increases. RAID 1 (A) provides protection through simple mirroring of data across paired drives, and while it can tolerate a single drive failure per mirrored pair, it does not guarantee survival of two simultaneous failures unless, by chance, both failures occur in different mirrored pairs, making it an unreliable choice for a guaranteed dual-failure requirement. RAID 0 (B) provides no redundancy at all, since it purely stripes data across disks for performance with no parity or mirroring, meaning even a single disk failure results in total data loss for the array. RAID 5 (D) uses only a single parity set and can tolerate exactly one drive failure; a second simultaneous failure results in data loss. RAID 6 is correct.
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