Abstract: Replication is a common method used to improve the data access reliability and system fault tolerance in the cloud storage system.It is one of the most important topics to reschedule the replicas distribution dynamically according to the changes of users’ requirements and environment in the replicas management.However,current replicas redistribution strategies mostly focus on the new replicas schemes,such as replicas number and their placements,on the pre-mise that it can be completed automatically,without taking into account the task scheduling problem in practice.In fact,data replica distribution transition is a complex scheduling problem involving data replicas migration and deletion among data centers.In addition,the required disk space and time of different scheduling strategies have large differences,lea-ding to big difference in cost and efficiency.In this way,this paper first proposed a data replicas distribution transition model and feasibility analysis in the cloud storage environment.Also a minimum-cost data replicas distribution transition problem definition was presented,and then its complexity was proven based on 0-1 Knapsack problem.Besides random strategy,three transition strategies (MTCF,MOCF and MTCFSD) were given from minimum-cost view.In the end,a series of experiments were performed on CloudSim simulation platform.The results show that nearly 60% of transmission number and 50% of transmission cost are reduced compared with other methods,indicating the proposed method’sreliability and effectiveness,so as to further improve the cloud storage system performance.

Key words: Cloud storage system, Cost, Distribution transition, Replicas, Tasks scheduling