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Time Machine could not complete the backup.

Files can’t be copied onto the backup disk because it appears to be read-only.

You may need to repair or reformat the disk using Disk Utility. If the disk can’t be repaired, you must use a different disk for backups. Open Time Machine preferences to select a different backup disk.

Why is Time Machine insisting my drive is Read-only, when in fact it isn't?

This is becoming a routine occurrence. What's troubling is the problem is easy enough to resolve by simply unmounting/mounting the Time Machine drive and selecting Back Up Now from the menu and it purrs like a kitten.

After performing the step outlined above, my latest Time Machine backup is tucked neatly away and everything is fine once more.

24-inch iMac 2.8GHz (early 2007)-OTHER, Mac OS X (10.7.2)

Posted on Mar 24, 2012 3:48 PM

50 replies

TinMass

Level 1

1 points

Jan 17, 2014 11:34 AM in response to G4Dualie (Michael)

Yeah me too... Have same OWC also

Apr 26, 2015 4:36 PM in response to wilvo

Same problem here. Time machine recently started giving me fits, despite my repairing and then ultimately erasing the drive and trying to start over. Then I found this thread… When I tried to run the script, my computer told me to use "diskutil mountDisk /dev…" or "diskutil unmountDisk /dev/..." It seems to work. I don't know how to open an application from Calendar though, so maybe I'm going to have to run this thing manually.

nancydee

Level 1

4 points

Jun 24, 2015 8:07 PM in response to Pondini

Thanks. This helped me very much. I had a 2 T WD that would not back up in my Time Machine, error=read only. This happened all of a sudden as it worked just fine for four years.

Ran out to purchase a new 6T to remove files. The the 6T would not back up in the Time Machine. I did what you recommeneded, ejected 6T, Shut down Mac Book Pro, restarted MBP, connected 6T and it finally backed up! Thanks,

Nancy D'Agostino

dwmusic

Level 1

10 points

Nov 29, 2015 10:59 AM in response to G4Dualie (Michael)

I have this issue too. Apple's Time Machine Preferences page flatly and completely unhelpfully informs me "Time Machine could not complete the backup." No reason given, and so taken at face value, can only mean nothing can be done and I wasted my money buying a 2TB drive dedicated to Time Machine backup. Formatting the disk anew every time I want to do a back is ridiculously time wasting, since it can take over a day to complete. I may as well just manually copy the files (which is what I have chosen to do, using the very same drive). The Apple message only tells me that their Time Machine software doesn't work. The WD Firewire 800 drive has passed all Disk Utility tests, and the source drive likewise, including yet another "Repair disk permissions" yawn, which has never once run clear on any drive I ever used with any Apple OS.

defaria

Level 1

4 points

Mar 30, 2016 4:37 PM in response to Pondini

If TimeMachine marked it read only because it saw problems with the drive then the only correct response would be for TimeMachine to report that very fact, not the red herring of read-only.

Time Machine could not complete the backup.