MacOS – Macbook Air – Deleting large files but not getting back the space

The current version of Time Machine keeps two types of backups. There are backups that are stored on your computer as well as network backups that are stored on your networked storage (time-capsule, NAS, etc). You can see these by entering Time Machine and looking at the timeline ticks to the right. The pink/purple ticks are network copies and the white ticks are the ones on your local computer. The local backups occur when your network storage is not available, also they may occur more often than the 1hr snapshots set for network backups. As your hard drive fills up, OS X will start to cut back the amount of space it uses for local backups. If you want to disable this feature and recover your local disk space, then open a terminal (Applications -> Utilities -> Terminal) and enter the following command followed by your password.

sudo tmutil disablelocal

This should turn off the feature and free up the space. You can turn it back on with

sudo tmutil enablelocal

It's likely in /Volumes/MobileBackups and you can easily delete it by entering Time Machine and navigating to the folder where the file existed. Select the file then command-click (right-click) and delete all backups of that file.

Normally, the system information window shows the backup space, but I have seen this window get hung up and not properly report storage space when Spotlight and/or the disk catalog are wonky.

You can also wipe all local backups by disabling the local store:

 sudo tmutil disablelocal

If the above steps doesn't work, you'll want to boot into recovery mode and run Disk Utility to check that the directory structure and file system catalog are correct. A fsck -fy / in single user mode is also equivalent if you are so inclined to fix things from terminal or want to perform a safe boot and have the system clean things up systematically.