DRL logically divides a volume into a set of consecutive regions, and maintains a log on disk where each region is represented by a status bit. This log records regions of a volume for which writes are pending. Before data is written to a region, DRL synchronously marks the corresponding status bit in the log as dirty. To enhance performance, the log bit remains set to dirty until the region becomes the least recently accessed for writes. This allows writes to the same region to be written immediately to disk if the region's log bit is set to dirty.
On restarting a system after a crash, VxVM recovers only those regions of the volume that are marked as dirty in the dirty region log.