Research Of A RAID-5System Expansion Technique

Redundant array of independent disks improve the throughput of storage systemthrough striping and improve reliability through data redundancy. As the available spacebecome smaller and smaller while using, we need expansion for the disk array.In the expansion process, it’s very inconvenient for the user that all the data of the diskarray need to be migrated and user can’t use the disk array during the process.The online expansion will not affect the normal use of the disk array and guarantee theconsistency of the data. We invent a new expansion algorithm on the basis of existingonline expansion algorithm. It reach the theoretical minimum amount of data migrationand use a new data distribution instead of the standard way. It does not undermine thereliability and performance of the disk array.In the data migration process, the speed control mechanism ensure the rationality ofthe online expansion. When the workload of the system is high, we lower the speed of datamigration to ensure high response to the user request. When the workload is low, weaccelerate the speed of data migration so that the expansion can be finished soon.Meanwhile, we maintain an expansion window in the process in order to ensure theconsistency of the data. Different ways are used to deal with the request of user accordingto its relationship with the expansion window.We test the system in offline and online ways. The test results show that the newexpansion algorithm can get a better expansion time than the standard way in case ofoffline expansion. In case of online expansion, speed control mechanism play a good roleto get a higher response to the user request than normal way, while the expansion time isalso better. After expansion, the new data distribution work get almost a equalperformance compared to standard way.