PDRS: A New Recovery Scheme Application for Vertical RAID-6 Code

As the technique developing, some important problems in storage systems have been solved appropriately. A good example is the development of RAID-6 code techinque, the appear of it has greatly improved the reliability, availability of modern storage systems. Some best known vertical RAID-6 code like P-code and X-code has acquire optimal or near optimal performance in encoding, decoding and update. But they do not detailedly analysis the status of reconstruction with single-disk failure. In the status, there are many paths to perform reconstructing. But the path you choice will greatly affect the performance of whole storage system. Based the phenomenon found above, we present a fast and effcient scheme, Path Directed Recovery Scheme (PDRS for short), to find a optimal path to reconstruct single-disk failure in P-code and X-code. Using PDRS, we will acquire some benefits: (1) it can decrease the disk I/O complexity caused by reconstruction and therefore accelerating the speed of reconstruction, (2) it can balance the load on each disk, consequently can avoid the hot problem in a degree. We perform theoretical analysis and evaluation of the PDRS when applied in P-code with (p-1)-disk and X-code with p-disk. Our theoretical analysis shows that PDRS applied in P-code with (p-1)-disk can acquire up to 25% performance improvement. To verify the effectiveness of PDRS, we have conducted intenvice simulation. The simulation results shows that PDRS applied in P-code with (p-1)-disk can speedup the recovery duration by up to 23.6% under spare-rebuilding mode. Overall, PDRS is a efficient and useful recovery scheme that can applied to all of the vertical RAID-6 code.