Time Machine could not back up the disk

How much free space do you have on your boot drive? If it's too small to create local backups Time Machine will give that error message.

Control (right) - click on the boot drive and select Get Info from the contextual menu. The Info pane will tell you the amount of free space left.

No, it shouldn't be too small. Try running First Aid on the TM drive with Disk Utility. It'll take much longer than on other drives due to the complex ecosystem of permissions and hard links. Also run First Aid on your boot drive.

Hello there, erahi!

Thanks for stopping by the Apple Support Communities. We understand that you are having trouble backing up your computer with Time Machine, as you are receiving an error message. We'd be happy to help!

Based on what you've described, we would begin by using the Apple Support article Time Machine troubleshooting on Mac - Apple Support.

Don't hesitate to respond back if you still need some help!

Cheers.

Thank you Old Toad

The First Aid on both disks helped! It really took long time. Checked the Boot Drive in Recovery Mode.

No errors were reported.

Cheers,

Egils

I have the same issue.

Time Machine couldn't complete the backup

Time Machine could not back up the disk iMacHD Data because it is nearly full

Delete some files on this disk and try again

I have 3TB Fusion drive, with 1.12TB available, and two 8TB TM drives one with 3.64TB available, and the other with 2.49T available

suddenly two days ago, it stopped backing up to either TM drive

I run disk first aid on both, no issue, same for the Fusion drive

any idea?

-avi