Abstract: Erasure coding consumes less storage space and obtains a higher data reliability,thus being widely used by distributed storage systems.However,when erasure codes are used to repair data,their high repair costs limit their application.In order to reduce the repair cost of erasure codes,researchers have researched a lot on block codes and regenerative codes.But block codes and regeneration codes are passive fault tolerance.For some nodes that are prone to failure,using active fault tolerance can better reduce repair costs and maintain the system reliability.Therefore,this paper proposes a proactive basic-Pyramid(PPyramid) code.The PPyramid code uses the hard disk failure prediction method to adjust the association between redundant and data blocks in the Pyramid code,divides hard disks that are predicted to fail into the same group,thus making all read operations to be performed within the team when recovering data,thereby reducing the number of read data blocks and saving repair costs.In a distributed storage system based on Ceph,it is compared with other commonly used erasure codes,when repairing multiple hard drives.Experimental results show that,PPyramid codes can reduce repair costs by 6.3%~34.9% and decrease repair time by 7.6%~63.6% compared with basic-Pyramid.Compared with LRC code,pLRC code,SHEC code and DLRC code,it can reduce repair costs by 8.6%~52% and decrease repair time by 10.8%~52.4%.Meanwhile,PPyramid codes are flexible in construction and have strong practical application value.

Key words: Data repair, Distributed storage system, Erasure codes, Failure prediction, Hard disk failure