Apple Tips:  Using Disk Utility

10.  If a disk doesn't appear in the sidebar

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This applies only to directly-connected external disks (ie, connected to your Mac via USB, FireWire, Thunderbolt or eSATA cable).  

  1. If you have an external drive connected to another Mac, a Time Capsule, or an Airport Extreme, connect it directly to your Mac to use Disk Utility on it.

  2. If you have Time Machine backups on a Time Capsule or 3rd-party NAS (Network Attached Storage) drive, see Time Machine Troubleshooting item #A5.

  3. If you have a Time Capsule or other network disk containing data other than Time Machine backups, you cannot use Disk Utility on it. 

  4. If an internal disk doesn't appear, contact your nearest AppleStore or Apple Authorized Service Provider.


If your disk doesn't appear in Disk Utility's sidebar, the disk may have failed, or there may be a problem with the power or connection to it.

  1. Be sure all plugs are snug and secure, and the cable isn't worn or frayed.

  2. Connect the drive directly to your Mac -- no hubs or daisy-chaining (and not the USB port on a keyboard).

  3. Try different port(s), cables, and combinations of the two (a plug that works fine in one port may not make good contact in another).  If you only have one cable, try swapping ends.  

  4. If the disk has a separate power connection, make sure that plug and cable are snug and secure, too, and plugged-in to a known good outlet.  It's best to plug it into a good surge protector, and better to plug it into a U.P.S. ("Uninterruptible Power Supply" -- battery backup) system. 

  5. If the disk is "bus-powered" (gets power from your Mac instead of a separate power plug), disconnect as many other devices as you can to provide as much power as possible. 

  6. Disconnect the drive for several minutes. Restart your Mac, reconnect, and try again. 

  7. Try connecting it to another Mac.


If it still won't appear, it's almost certainly failed.  Contact the maker or supplier.  If it has a separate power supply, it's possible that's failed and the disk itself is ok.

But remember, disk drives DO fail.

In fact, they all fail, sooner or later.  According to a Google study, the odds of a disk failure are:

  1. 1 in 25 for year 1

  2. 1 in 10 for year 2

  3. 1 in 5 for year 3

  4. 1 in 4 for year 4

  5. 1 in 3 for year 5.