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A local backup is one that is connected directly to your computer via an external storage device.   The external drive you intend to use for your Time Machine backup should be at least as large as your computer's hard drive and bigger if possible.   A Time Machine drive can be connected via USB or Firewire and should be formatted Mac OS Extended (Journaled).  If you are unsure if your drive is formatted correctly, call the Technology Services desk at 471-1199 and a technician can help.

Technology Services recommends that you designate an external drive exclusively as a Time Machine backup and routinely have it plugged into your computer.    Time Machine cannot run if the local drive is not connected.  Using your Time Machine drive for other purposes other than backups runs the risk of it becoming too full or not being available for backup when you most need it.
 

The first time Time Machine runs, it takes awhile to get a baseline backup. During that time, the computer may seem sluggish.  Although Time Machine can be interrupted and picks up where it last left off, a best practice is to start this process when the computer will have plenty of time to complete the task.  Depending on the amount of data you have on your hard drive, this could take awhile.  A good time to start the initial backup is at the end of the work day or overnight.  

When you plug the drive into your computer and turn it on.  If Time Machine is already active on your computer but not configured for a particular drive, you should be presented with a prompt may be prompted asking if you'd like to use the drive you just plugged in as a Time Machine backup.  If you do not get this option, open Time Machine preferences by going to the Apple Menu and choosing System Preferences.   Look for the Time Machine is located in System Preferencesicon. 

Alternatively, if your Time Machine preferences were set to display in the Apple menu bar, you can navigate to the upper right corner and choose the "Open Time Machine Preferences" option from the pull down menu.  The Time Machine Apple menu icon looks like an analog clock with a circular arrow frame.

The Time Machine preferences window is straight forward and simple.  If Time Machine is off, slide the "switch" to the on position.  The top button will either have the wording, Select Disk or Change Disk.  Click it and you should be presented with a list of available storage solutions that Time Machine can use.  Typically the only thing that will be listed is the drive you just plugged in.  Highlight the desired drive and select Use for Backup.  (The Set Up Time Capsule button is for use with home Apple Airport Extreme and Time Capsule wireless routers.)

An option in the Time Machine preference window is a checkbox for showing the Time Machine status in the menu bar.  Check this and you'll notice the Time Machine icon in the Apple menu bar at the upper right of your screen.  

Other options are shown by clicking the Option button.  Here you can choose The Options button allows you to change settings to skip certain directories (iTunes for example) to make your backup smaller.   If your external hard drive is larger than your computer's drive, then don't worry about being selective.

That's it.  Once you have clicked the Use for Backup button, Time Machine begins its backup within a few seconds.  You can close the Time Machine and System Preferences window.   As mentioned, the initial backup may take awhile.  You'll get a standard progress bar window but you may also notice the  icon for Time Machine spinning in the Apple menu bar.   Remember to have your external drive plugged in routinely and Time Machine will take care of itself.  It cannot backup if the drive is not present.

Besides hedging against a catastrophic computer failure, Time Machine allows recovery of files that were unintentionally deleted by a user.   For instructions on how to restore deleted files, please refer to the Apple article linked to above. http://support.apple.com/kb/ht1427 Mac 101: Time Machine.