Problem

Sometimes, you might see this trouble when you used Mac.

According to that article, re-indexing spotlight search is the solution, but I experienced Storage tab showed too much "Backup" value and I couldn't fix the problem though I tried to do that:

Of course, I don't have 170 Mac Pros (and no money to buy them), so this value must be incorrect!

Solution

1. Open your favorite terminal
2. Run sudo mdutil -i off /. This command means "Disable Spotlight Search Indexing at root directory". By running this command, Spotlight Search index will be deleted. Note that this step needs root permission because accessing to root directory needs the permission.
3. Disable time machine backup thru System Preferences > Time Machine. You can just toggle ON to OFF below "Time Machine":
4. If you already closed your terminal opened at step 1, re-open it, but you don't need to run the command at step 2.
5. Run sudo mdutil -i on /, which means "Turn on Spotlight Search Indexing at root directory". By doing this, the index will be created. This step also needs root permission for the same reason as step 2.
6. Take a rest for 1-2 hours.. or more :)
7. Until this step, the Storage tab shows the value like this: (I have Virtual Disk Image and exclude the path. Therefore this is correct)
8. Turn on Time Machine Backup. However, you should remove previous backups and take full-backup.
9. Take more rests...
10. The problem must be fixed!