Bit map write logging with write order preservation in support of asynchronous update of secondary storage

摘要

A method for maintaining a bit map of data writes, the method including associating each of a plurality of bit groups in a bit map with a different one of a plurality of segments of a data storage device, where each of the bit groups includes a plurality of bits, and setting any of the bits in any of the bit groups to indicate that any portion of the segment corresponding to the bit group has been written to, where the write order of any two of the plurality of segments that have been written to is preserved by their corresponding set bit groups.