1. A method for migrating a selected set of virtual machines from a first volume to a second volume, comprising: receiving a list of virtual machines which are not migrating from a first volume to a second volume; accessing a host file system usage map of a host machine that indicates active blocks out of a plurality of blocks of the host file system on the first volume; accessing a plurality of virtual file system usage maps of a plurality of virtual machines that indicate active blocks of the virtual file systems out of a plurality of blocks of the first volume; generate a filter usage map that identifies the active blocks of the virtual machines which are not migrating, and based on the virtual file system usage maps and the host file system usage map; migrating the plurality of virtual machines from the first volume to the second volume, wherein the active blocks of the virtual file systems which are not migrating are skipped in accordance with the filter usage map; and processing metadata at the second volume to properly reflect the virtual machines which were not migrated.