Abstract: Method and apparatus for managing concurrent access among computers to a bitmap stored on disk storage. In some examples, a command is received from a requesting computer of the computers, the command indicating that one or more bits in the bitmap are to be cleared. The bitmap as stored on the disk storage is updated responsive to the command to clear the one or more bits in the bitmap. Synchronization data associated with the bitmap is stored. The synchronization data is configured to distinguish between a current generation and a previous generation of the bitmap, and to specify an action to be performed in response to receiving a subsequent command for accessing the bitmap if the subsequent command identifies a previous generation.