The Provisioning Server treats a vDisk image file like a regular file, but the target device treats it as a hard drive. The procedure for backing up a vDisk image file is the same as backing up any other file on your server. If a vDisk image file becomes corrupt, to restore it requires simply replacing the corrupted file with a previous, functional version.
Do not back up a vDisk while it is in use or while it is locked. It is recommended to integrate the backing up of vDisks into your normal Provisioning Server backup routine.