Time Machine won't backup anymore

Hello fishysammay,

Welcome to Apple Support Communities!

We want to help get Time Machine backing up your Mac again.

Let's make sure you've taken these steps first to help isolate the issue:

"If Time Machine says that it can't use your backup disk to back up or restore your files, try these solutions.

• Make sure that you're using a backup disk supported by Time Machine.
• Unless you're using a network backup disk, make sure that your backup disk is connected directly to your Mac, not through a USB hub or other device.
• If your backup disk is connected directly to your Mac, use Disk Utility to repair the disk.
• If you're using a network backup disk, make sure that the network connection is good and your Mac is connected to the same network as the backup disk. If you completed a previous backup successfully, verify that backup: Press and hold the Option key while choosing Verify Backups from the Time Machine menu in the menu bar.
• Make sure that the firmware of your backup disk is up to date. Check with the manufacturer of the backup disk for details.
• If no other solutions work, start over: Erase your backup disk, then use Time Machine to select it as your backup disk again."

This Apple Support page has the full details: If you can't back up or restore your Mac using Time Machine - Apple Support

Since the error is saying the disk needs to be erased, you can find that step under the last bullet above.

We hope this helps to resolve the error so you can continue to backup again after erasing the disk.

Cheers!

fishysammay wrote:

I could try getting a second drive (one for each Mac, like you suggest). Any thoughts to why there was no problem for the last two years and then it became a problem 2 months ago?

Thanks.

Sam

See this information: Types of disks you can use with Time Machine on Mac - Apple Support

Several points relative to this:

Time Machine basically takes over the entire drive for backups. "The entire APFS volume is reserved for Time Machine backups." If something else (like another computer) is also accessing the drive, as APFS needs more and more space for backups, it eventually creates a conflict between the two (in your case you have two computers each thinking it has the entire drive for its Time Machine use) and one or the other of the two computers will be displaced. This conflict could have caused your error message. Not sure if it did but it could have.

Also, if you are using a network drive, that adds another complication. Apple says you should use SMB to back up over a network. Some network drive manufacturers claim to implement SMB but don't do it properly. There are lots of posts about that in Apple Discussions. The symptoms reported are that the backups work for a while, and then stop working. Or, even worse, when trying to restore from a network drive backup, the restore fails.

How is your network drive set up?

I recommend that you simply connect separate external Time Machine backup drives directly to each Mac and use those as drives dedicated to Time Machine. The scheme you are using is vulnerable on multiple fronts. It is essential to have a reliable method for backups.

fishysammay wrote:

My wife's MacBook is also set to back up to the same WD external drive through Time Machine and her computer is not having any trouble. My trouble just started about 2 months ago. Any help is greatly appreciated.

that may be the issue. backing up more than one Mac to the same external drive is not recommended, and can sometimes be problematic. and as affordable as external drive have become, I would use a separate dedicated drive for each Mac.

fishysammay wrote:

Any thoughts to why there was no problem for the last two years and then it became a problem 2 months ago?

if I had to guess, did you update / upgrade either or both machine's macOS 2 months ago?