Time machine backup fails with "Two of the disks to back up have the same name. Rename one of the disks named XXX"

Hey there,

Thanks for reaching out to Apple Support Communities. We understand that you're having issues backing up your device via Time Machine. Let's perform these steps while booted to the internal drive (not when booted into Recovery)

1) Open Disk Utility from /Applications/Utilities

2) Within Disk Utility select one of the Macintosh HD - Data volumes in the sidebar and look at the (minus) button. If this button is greyed out and not clickable then we are looking at the active Data volume. If the (minus) is clickable then we are looking at the extraneous volume that can be removed. Click the (minus) button after identifying the extraneous volume.

3) Attempt Time Machine backup

If you continue to experience issues, please reach out to us here: Contact Apple Support

Have a great day!

A simple restart actually fixed this issue for me. It started after I reset the System Manager Controller to fix a battery service warning, so wondering if that triggered this backup issue since I'd been able to backup on Catalina without problems beforehand.

I'm having the same issue, but neither "Macintosh HD" and "Macintosh HD - Data" can be deleted—the function is greyed out.

Same here. Have both partitions. Neither are minus-able.