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.
