Time Machine Troubleshooting - Backup Volume Could Not Be Mounted

What to Do When a Time Capsule or NAS Volume Is Unavailable

Turn Time Machine off, then use Select Disk to reselect your remote backup drive. Screen shot courtesy of Coyote Moon, Inc.

Time Machine, Apple's popular backup app, isn't limited to working with backup volumes that are physically attached to your Mac. It supports remote backup drives in the form of networked drives, including Apple's own Time Capsule product.

Network-based Time Machine volumes are very useful. Having your backup drive in a remote location, one that's physically isolated from your Mac, protects your backups in the event your Mac has a catastrophic failure.

Another wonderful use for remote Time Machine volumes, such as Time Capsules or NAS (Network Attached Storage), is to allow multiple Macs to perform backups to a single central location.

Of course, network-based Time Machine volumes have their own set of problems; one of the most common is the failure of the backup volume to mount on your Mac. This prevents Time Machine from accessing the remote volume, and usually results in the following error message:

Backup Volume Could Not Be Mounted

There are variations of this error message that you may come across, including:

Backup Disk Image Could Not Be Mounted

This error message and its variations are nicely descriptive, letting you know the problem is likely with the remote backup volume. Correcting the problem is usually simple; below I outline the most likely causes.

Power:

It may seem obvious, but make sure the Time Capsule or NAS has power, and that any appropriate indicators are lit.

Network connection:

If you're having problems with a Time Capsule or NAS, make sure they're available on your network. If you're using a wireless network, you can check your basic Wi-Fi connection with Use Wireless Diagnostics App to Fix Your Mac's Wi-Fi Issues.

Check your NAS manual for instructions on how to confirm that the NAS is present on your network.

For Apple's Time Capsule, do the following:

  1. Launch Airport Utility, located in your /Applications/Utilities folder.​
  2. AirPort Utility will scan for Apple wireless devices, including a Time Capsule. If Airport Utility displays your Time Capsule, then it's powered on and accessible to your Mac. If you don't see your Time Capsule displayed, try powering it off and then back on again. If you still can't access your Time Capsule, you'll need to try resetting it to its factory defaults. You'll find instructions for how to do this in the Time Capsule Setup Guide.

Password incorrect:

Time Capsule and most NAS products require a password to be provided before the network drive will mount on your Mac. If the password supplied automatically by Time Machine to your Time Capsule or NAS is incorrect, you will see the "Backup volume cannot be mounted" error message. This is actually the most common reason for seeing this error message.

It usually means that the administrator of the Time Capsule or NAS changed the password and forgot to update all of the information for Time Machine users. If that's the case, you can either return the Time Capsule or NAS password back to what it was when Time Machine last worked, or update the password on your Mac.

To update the password on your Mac, follow these instructions:

Reselect Time Machine Backup

  1. Log in to your Mac with an administrator account.​
  2. Launch System Preferences by clicking the System Preferences icon in the Dock, or selecting System Preferences from the Apple menu.​
  3. Select the Time Machine preference pane in the System Preferences window.​
  4. Turn Time Machine off by clicking the Off slider.​
  5. Click the Select Disk button.​
  6. Browse to your Time Capsule or NAS drive, Select it as the Time Machine volume, and supply the correct password.​
  7. Turn Time Machine back on.
  8. It should now be able to perform backups.
  9. If you still have problems, you can try changing the password that's stored in your keychain.

Change Keychain Password

  1. Turn Time Machine off.​
  2. Launch Keychain Access, located in /Applications/Utilities.​
  3. In the Keychain Access window, select System from the sidebar's keychain list.​
  4. Locate the keychain entry whose name starts with the name of your Time Capsule or NAS. Example: If your Time Capsule's name is Tardis, its keychain name will be Tardis.local or Tardis._afpovertcp._tcp.local.​
  5. Double-click the keychain entry for your Time Capsule or NAS.​
  6. A window will open, displaying various attributes of the keychain file.​
  7. Click the Attributes tab, and then place a check mark in the Show Password box. Supply your admin password to authenticate your access.​
  8. The password for your Time Capsule or NAS will display.​
  9. If the password isn't correct, enter the new password in the Show Password field, and then click Save Changes.​
  10. Quit Keychain Access.​
  11. Turn Time Machine on.

You should now be able to successfully perform a Time Machine backup to your Time Capsule or NAS.

More From Us