Two of the disks to back up have the same name

I recently got a problem on my Mac with Time Machine. Time machine is a wonderful tool used to backup the full hard drive, but incrementally and element by element. That means you are able to restore a specific file at a specific date.

This error looks very common and most of website explain that a partition is duplicated and it can be fixed using Disk Utility. That’s maybe true, but not all the time.

First, unplug all the external drives from your Mac, to don’t do any mistake and open the terminal.

sudo -i
ls -la /Volumes

Just remove the directories named like your Time Machine disk(s) and it will fix the problem.
Even with the hard drive disconnected, on my Mac is had:

Virgils-Mac:~ root# ls -la /Volumes
 total 0
 drwxr-xr-x   5 root  wheel  160 Mar 17 09:52 .
 drwxr-xr-x  23 root  admin  736 Feb  5 09:12 ..
 lrwxr-xr-x   1 root  wheel    1 Mar 13 17:23 Macintosh - Sys -> /
 d--x--x--x   2 root  wheel   64 Mar 13 17:23 backup
 drwxrwxr-x   6 root  wheel  272 Mar 16 15:09 timemachine

To remove the directories, use rmdir

rmdir /Volumes/directorytoremove

So in my case:

rmdir /Volumes/backup /Volumes/timemachine