One problem you may encounter with Time Machine occurs when you see an error message that says, “The backup volume is read-only.” Despite this message, your backup files are probably in good working order, and no backup data has been lost.
Causes of Time Machine Read-Only Error
The cause of the read-only error message depends on a few factors, but in most cases, the Mac thinks that the drive permissions were changed to read-only as a result of a power outage. It’s unlikely that you accidentally set the drive to be read-only.
Fixes for Time Machine Read-Only Error
You can’t back up new data to a Time Machine drive that displays the read-only error until the problem is fixed. A few possible fixes exist for this problem, and each takes only a short time to try.
Eject the external backup drive. If you use an external drive connected to a Mac by USB, FireWire, or Thunderbolt as your backup drive, eject the drive from the Mac. Then reconnect the drive and restart the Mac. This is the most common solution for the Backup Volume Is Read-Only error. If ejecting and reconnecting an external drive doesn’t help, don’t reset the permissions because this won’t do any good. Instead, follow these additional troubleshooting steps. Unmount the backup drive. If the drive cannot be ejected from the desktop, unmount it using Disk Utility. Repair the drive. If ejecting or unmounting the backup drive doesn’t fix the problem, the Time Machine volume may have disk errors that need to be repaired. Turn off Time Machine in System Preferences > Time Machine and use Disk Utility to run First Aid on the Time Machine backup drive. When the process is complete, exit Disk Utility and turn on Time Machine in the System Preferences.
When the repairs are complete, you should no longer encounter the Backup Volume Is Read-Only error message, and your backups proceed as scheduled.
If ejecting and reconnecting an external drive doesn’t help, don’t reset the permissions because this won’t do any good. Instead, follow these additional troubleshooting steps.
When the process is complete, exit Disk Utility and turn on Time Machine in the System Preferences.
Is It OK to Use a Drive That Needed Repairs for Time Machine?
In most cases, this one-time problem is unlikely to have any effect on the reliability of your Time Machine drive. As long as the Time Machine drive doesn’t continue to have problems that require Disk Utility or a third-party drive utility app to repair the drive, you should be fine.
In all likelihood, this was a one-time event, perhaps caused by a power outage or the Mac or Time Machine drive turning off unexpectedly.
As long as the problem doesn’t repeat, the Time Machine drive should be in good shape. However, if the problem reoccurs, it’s time to consider a repair to your existing drive or get a new drive to store your backups. Make an appointment at a nearby Apple Store or Apple Authorized Service Provider for repair or replacement advice for the drive.
