1. A method for providing an on-disk structure of a file system executing on a storage system including one or more disks, the file system capable of generating snapshots and providing fast sequential read access to a data container stored on the disks, comprising: arranging sequential portions of the data container into a plurality of regions on the disks, each region including a predetermined amount of disk space represented by blocks on the disks; organizing the plurality of regions as a plurality of active regions and other regions, each active region allocated for a different sequential portion of the data container and configured to store active file system data and snapshot data for the different sequential portion of the data container, wherein first blocks in a portion of the active region are marked as one of active for use in an active file system, active for use in one or more snapshots, and free; if an active block is not required by the one or more snapshots, overwriting the active block within the active region with new active data; and if the active block is required by the one or more snapshots, preserving the active block to become a snapshot block of the data container, and writing the new active data to any block marked as free in the active region.