Efficient access to storage devices with usage bitmaps

摘要: Upon receiving a request to allocate storage region, device may initialize the contents of default values (e.g., zero) in order avoid problems arising from unknown data stored locations region upon writing set location involved mirroring relationship, uninitialized corresponding mirror result mismatch that jeopardizes written data). However, initializing be time-consuming and inefficient. Instead, usage bitmap generated that, for respective sets indicates whether exist location. A read fulfilled by examining determine specified location, if not, value returned without accessing device. Other efficiencies also achieved using bitmap.