一种远程备份数据虚拟重构方法
A virtual reconstruction method for remote backup data

针对目前常用的基于写时拷贝（COW）快照方法的持续数据保护（CDP）系统在数据重构时，需要在快照物理空间存储旧数据，从而花费巨大空间和时间代价的问题，本文提出了一种远程备份数据虚拟重构方法.该方法使用偏移文件和位图文件分别记录旧数据块所在位置以及数据块是否变化，并在内核层创建虚拟块设备，自定义块设备的I/O处理函数，把对数据块的读操作重定向到镜像卷或日志卷，从而克服了快照方法造成的灾备中心时空资源浪费严重的问题.实验结果表明，相比基于快照方法的数据重构，本文方法不进行物理重构，不仅可有效地节约存储空间，而且可大幅地缩减数据重构的时间.
The method based on Copy On Write (COW) snapshot is mostly used to do data reconstruction in Continuous Data Protection (CDP) system, this method needs to store old data blocks in physical space of snapshot which will cost lots of space and time. Against to this problem, we present a virtual reconstruction method for remote backup data, our method uses a offset file to record the location of old data blocks and uses a bitmap file to record whether data blocks have changed or not, and then create a virtual block device in kernel with it’s own I/O request function which redirects all the read operation on data blocks to Mirrored Volume or Log Volume, thus overcomes the problem caused by snapshot method that resource in the backup center is extremely wasted. The experiment proved that our method without physical reconstruction can not only save more storage space efficiently but also reduce the cost of time during data reconstruction substantially