Research And Implementation Of Online Capacity Expansion And Snapshot Technique In RAID

With the the rapid development of information technology and popularity of emerging digital technologies, the demands of data high availability and safety are pushing the storage technology development. On the premise of uninterrupted data availability, how to online increase storage system capacity, backup and recovery important data have become the focus of research.RAID is the base device for storage systems and online capacity expansion is an essential function of it. Online capacity expansion function can add additional disks into RAID without suspending normal requests. Synchronization mechanisms are adopted to guarantee the data access consisitency in the expansion window. Data are redistributed to all disks in accordance with the new array configuration. Its validity has been proven by experiments.Snapshot is a popular technique for online hot backup. Since RAID can only tolerate disk hardware failure, adopting snapshot in RAID can avoid data loss caused by user errors, virus attacks etc. Copy-On-Write (COW) is a common used snapshot technique because of instantaneous creation and small capacity occupation, but its write performance was poor. With the careful analysis of COW write procedure, an asynchronous thread is proposed for writing snapshot block to snapshot volume. Normal write request response time can be reduced. This improved COW snapshot technique has been implemented in RAID. Its snapshot volume is preserved and uses hash table lookup to find copyed blocks. Numerical results show that improved COW can further enhance the performance and availability of RAID.