 <p>Creating snapshots in VHD works by putting an overlay over the existing VHD image, so that any change get written into the overlay file instead of overwriting existing data. For reading the top-most data is returned: either the data from the overlay if that sector/cluster was already over-written, or from the original VHD file if it was not-yet over-written.</p> <p>The vhd-util command creates such an overlay-VHD-file, which uses the existing VHD image as its so-called "backing-file". It is important to remember, that the backing-file must never be changed while snapshots still using this backing-file exist. Otherwise the data would change in all those snapshots as well (unless the data was overwritten there already.)</p> <p>The process of using backing files can be repeated multiple times, which leads to a chain of VHD files. Only the top-most file should ever be written to, all other files should be handled as immutable.</p> <p>Reverting back to a snapshot is as easy as deleting the current top-most overlay file and creating a new empty overlay file again, which again expose the data from the backing file containing the snapshot. This is done by using the same command again as above mentioned. This preserves your current snapshot and allows you to repeat that process multiple times. (renaming the file would be more like "revert back to <strong>and</strong> delete last snapshot".)</p> <p><strong>Warning:</strong> before re-creating the snapshot file, make sure that no other snapshots exists, which uses this (intermediate) VHD file as its backing file. Otherwise you would not only loose this snapshot, but all other snapshots depending on this one.</p>