Here's the error message I get: "An error occurred while copying files. The problem may be temporary. If the problem persists, use Disk Utility to repair your backup disk." When I try to follow that instruction, I'm informed that Disk Utility is unable to unmount the backup drive. This happens whether I have Time Machine turned on or off, and following ejecting and reconnecting the drive. Selecting Time Machine from System Preferences doesn't make any difference.

I'm running Yosemite 10.10.5 on a MacBook Pro 2.2 GHz Intel Core i7. My backup drive is a one-month-old My Passport for Mac, 1TB, which has been working perfectly up till now. Backups are using less than 1/10th of its capacity. It doesn't respond to my attempts to "get info," but I'm able to enter Time Machine OK.

Grateful for any help you can offer.

2 Answers 2


I've had this problem before. I think it is because the data is corrupt. What you need to do is restore the drive and create a new one. The easy way is to get a different computer and reformat it there, but if not, don't worry. Just go into Disk Utility and attempt to restore/reformat the drive. If it gives you an error like "Can't unmount the disk", follow this guide to forcefully unmounting a Time Machine backup disk. Then, you will have to setup a new backup.

Note: If your drive still gives problems after this, it may be broken and you may need to purchase a new one.


The drive could be failing. Try to format again with disk utility , setup time machine backup then start creating full backup again.

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