Time Machine read-only?!

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Level 1

100 points

Time Machine read-only?!

I've been struggling for the past few hours with an external Time Machine volume to which Mojave tells me that it cannot backup because it is read-only. I apologize, the exact error message is no longer available.

I've been trying the suggestions in this article (https://www.lifewire.com/fix-time-machine-errors-2259975) although not in the same order, as I discovered it after starting First Aid in Disk Utility. Disk Utility took a long time to run before failing with an error message. I can confirm that fsck_hfs was running for the whole time, having accumulated approx. 22 minutes CPU time. As I had already turned off Back Up Automatically in Time Machine preferences, I next tried disconnecting the volume, turning off the MacBook Pro, then connecting the volume and powering everything back up. Now I cannot convince Mojave to mount the volume. This is what I see in Disk Utility:

I cannot eject the volume, but neither can I see MacBook Pro 15 Time Machine on the Desktop, and Time Machine preferences, where I've turned on Back Up Automatically, says it will begin backing up as soon as MacBook Pro 15 Time Machine is connected. I saw that fsck_hfs was running, and suspecting that it is doing what I already tried in Disk Utility, force quit it. But any attempt dismount Media fails, as does any attempt to connect MacBook Pro 15 Time Machine, and once again I see that fsck_hfs is running.

Does anyone have any suggestions, other than reformatting the disk and losing more than a year of backups?

For the record, here are the specifications: MacBook Pro 15" 2018 model with Touch Bar, 32 GB RAM and 4 TB SSD running macOS 10.14.6 Mojave. The Time Machine disk is a LaCie P933 with 8 TB, purchased in Oct. 2018, just slightly after the MBP. It is connected to the MBP by USB-C.

MacBook Pro 15”, macOS 10.14

Posted on May 8, 2020 3:31 PM

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Answer 1

John Galt

Level 10

155,414 points

May 8, 2020 7:03 PM in response to Richard Liu

Does anyone have any suggestions, other than reformatting the disk and losing more than a year of backups?

The disk has already failed, although its Time Machine backup history may remain retrievable through persistent and repeated attempts to "repair" it with Disk Utility or fsck_hfs.

Since the disk has already failed attempts at reformatting it are also likely to fail. If you successfully reformat it, the same failure is certain to occur again, perhaps in a very short time. Purchase a replacement.

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Answer 2

Richard Liu Author

Level 1

100 points

May 9, 2020 1:51 AM in response to John Galt

Yeah, I was coming to the same conclusion. I just wanted to know whether the problem is hardware, or whether restarting the machine at the wrong moment could have cause a screwup. I've reformatted the disk and am now running the first Time Machine backup now. When it's finished, I may use TechTool Pro 12 to the check the volume surface.

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Answer 3

Richard Liu Author

Level 1

100 points

May 9, 2020 7:11 AM in response to John Galt

I did not assert otherwise. The backup is still running; Time Machine estimates 11 hrs. more. Businesses open again here in Switzerland for the first time since March 16 this coming Monday, and I've decided I won't even think about taking the disk back to where I bought before the hoards get over the novelty rambling around and infecting one another. So I can wait, and the unit is still under guarantee. If the backup completes, I'll run TechTool Pro and see whether it finds anything. That way, when I do take the disk back, I'll be able to say whether the problem actually is hardware.

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Answer 4

Richard Liu Author

Level 1

100 points

May 11, 2020 4:14 PM in response to Richard Liu

After the first backup on the newly formatted Time Machine disk I checked it thoroughly with TechTool Pro 12: Surface Scan, Partition Map, Volume Structures and File Structures. Surface Scan took approx. 19 hrs. but completed clean. Only File Structures found anything, a few hundred instances of a few invalid png files in an installation package. I suppose there could still be a problem in the making on the disk, but I'm inclined to think it was something that happened when I shut the machine down without waiting for Time Machine to quit. Besides, I would have a hard time invoking the guarantee on the basis that something happened that required the disk to be reformatted, and it might happen again, but right new a rather complete check of the disk turned up nothing. So I guess I'll just continue to use it.

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Answer 5

Richard Liu Author

Level 1

100 points

May 11, 2020 4:39 PM in response to John Galt

Yeah, 19 hours. It's 8 TB, as the MBP has 4 TB. Also, during the surface scan I apparently forgot to turn off Back Up Automatically in the Time Machine Preferences ... or accidentally turned it on. Paying closer attention might have reduced the 19 hours.

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