Disk image backup/restore with data preparation phase

A method for backing up data stored using a filing system on a computer non-volatile storage device is described. First pre-defined signature data is written, using the filing system, to substantially all of the unused portion of the computer non-volatile storage device. The data stored on the computer non-volatile storage device is then backed up, independent of the filing system. Data consisting of the first pre-defined signature is not backed up. In this manner, a backup is completed without access to the filing system, but which backs up only portions of the non-volatile storage medium which are in use.