Time Machine, will following plan work? A Time Machine usage plan as described below seems to meet our requirements. I kindly ask you for feedback if it will work. Any shortcomings if to compare it with Time Machine steady operation? It is external mass storage. Normally TM is off - OS X Preferences. Administrator connects TM external storage and enables TM in OS X preferences. Then the backup is started by invoking appropriate menu item. As soon as backup completes the external storage is disconnected and TM disabled in OS X preferences. Whole procedure is repeated once a week.