The default sleep settings in OS X 10.8 (Mountain Lion) cause the Mac to go to sleep while running a backup (either manual or scheduled) or a restore.

The screenshots in these instructions are for a desktop Mac. On a laptop, there are separate Energy Saver tabs for running on battery and on AC power. Backups and restores should be run with the Mac plugged into AC power.

1. Configuring sleep settings for manual backups and restores

Open the energy saver settings from [Applications] > [System Preferences] > [Energy Saver]. Ensure that [Put hard disks to sleep when possible] is not selected:

OS X 10.8 Energy Saver settings

2. Configuring sleep settings for scheduled backups

  1. Complete the steps under 1. Configuring sleep settings for manual backups and restores and keep the Energy Saver settings window open.

  2. If it is not already known, determine the scheduled backup window for the Mac.

  3. Click the Schedule... button in the Energy Saver settings window. A dialogue is displayed in which you can set the Mac to wake up before your scheduled backup window. Set the Mac to wake up five minutes before your scheduled backup window on the correct day and Click OK.

    OS X scheduled wake settings

  4. Drag the [Computer sleep] slider to set the time to stay awake. This needs to be at least as long as a backup takes. Start with a setting of one hour and adjust if scheduled backups do not complete.

3. Running manual backups and restores with the caffeinate command.

It is also possible to use the OS X caffeinate command to keep the Mac awake while running a backup or restore.

  1. Open a terminal by navigating to [Applications] > [Utilities] > [Terminal].

  2. Run the TSM client with the command:

    sudo caffeinate -is dsmj

  3. Proceed with the instructions for running a manual backup or restoring files.