A gracefully degradable declustered RAID architecture with near optimal maximal read and write parallelism

A new layout method, Prime-groups, is proposed to evenly distribute parity groups for declustered RAID. Prime-groups satisfies most of the layout goals for a good declustered RAID layout. For the goals that are not satisfied, it is near optimal. A new layout goal maximal write and reconstruction parallelism is also proposed. If a layout satisfies the new goal, all the surviving disks can be read in parallel and can be rewritten in parallel during reconstruction and reconfiguration. Prime-groups satisfies the new goal when the write request begins in the first disk of the array. It is also near optimal in term of declustering ratio when p is a prime. Prime-groups can compliment the layouts proposed by G.A. Alvarez et. al. (1996), as the criteria to obtain a good layout is quite different between Prime-groups and those proposed by Alvarez et. al