US Patent 7873601 Backup of incremental metadata in block based backup systems

Performing a backup is disclosed. A changed portion of a file system tree is determined based at least in part on a stored state of the file system tree at a time a prior block based backup of the file system tree was performed. Incremental metadata associated with the changed portion is obtained. The obtained incremental metadata is stored where there is at least some metadata associated with an unchanged portion of the file system tree that is not stored when storing the obtained incremental metadata.