A container file system is built on a sparse metavolume for enhanced decoupling of logical storage from physical storage and for providing common supplementary storage services for iSCSI block access and for NFS or CIFS file system access. The container file system contains a production file system or iSCSI LUN and may also contain snapshot copies of the production file system or iSCSI LUN. The container file system manages storage space among the production file system or iSCSI LUN and its snapshot copies, and also improves fault containment. The sparse metavolume provides thin provisioning of the container file system. A slice map indicates whether or not each slice of logical storage in the sparse metavolume is provisioned with an associated configured slice of data storage.