A Case for Continuous Data Protection at Block Level in Disk Array Storages
Weijun Xiao, Jin Xia Ren, Qing Yang · IEEE Transactions on Parallel and Distributed Systems · 2008
Abstract — This paper presents a study of data storages for continuous data protection (CDP). After analyzing the existing data protection technologies, we propose a new disk array architecture that provides Timely Recovery to Any Point-in-time, referred to as TRAP-Array. TRAP-Array stores not only the data stripe upon a write to the array, but also the time-stamped Exclusive-ORs of successive writes to each data block. By leveraging the Exclusive-OR operations that are performed upon each block write in today’s RAID4/5 controllers, TRAP does not incur noticeable performance overhead. More importantly, TRAP is able to recover data very quickly to any point-in-time upon data damage by tracing back the sequence and history of Exclusive-ORs resulting from writes. What is interesting is that TRAP architecture is very space-efficient. We have implemented a prototype TRAP architecture using software at block level and carried out extensive performance measurements using TPC-C benchmarks running on Oracle and Postgress databases, TPC-W running on MySQL database, and file system benchmarks running on Linux and Windows systems. Our experiments demonstrated that TRAP is not only able to recover data to any pointin-time very quickly upon a failure but it is also space efficient. Compared to the state-of-the-art continuous data protection technologies, TRAP saves disk storage space by one to two orders of magnitude with a simple and a fast encoding algorithm. In addition, TRAP can provide two-way data recovery with the availability of only one reference image in contrast to the one-way recovery of snapshot and incremental backup technologies.