An issue may occur on some Mac systems where after installing the OS X 10.10.3 update, the Finder and other services that report drive space may show an increasing level of available space. This may be accompanied by the Storage tab in the About This Mac window showing your hard drive’s space is being used only for backups.
In general, when this type of oddity appears in the About This Mac window, it suggests your drive’s Spotlight index needs to be rebuilt; however, this issue will likely survive a forced index rebuild. In addition, it being mirrored in the Finder’s status bar and information windows suggests the issue is not with Spotlight, but with another aspect of the system, namely Time Machine and the way that local snapshot backups are being handled.
Time Machine is primarily intended for use with an external storage drive, so large full-system backups can be maintained; however, it also supports a smaller local snapshot database that is stored on your boot drive. These local backups allow Time Machine to provide similar backup services for personal documents you create, when you do not have your dedicated Time Machine drive attached to your Mac.
This problem will likely need to be fixed by Apple’s engineers; however, you can attempt to override the issue by disabling local Time Machine backups:
- Open the OS X Terminal utility (in Applications > Utilities) in an administrative account
- Run the following command
sudo tmutil disablelocal
This command will not only disable the creation of local backups, but will also delete any that are on your system. This action should clear up the incorrect free space calculation on your Mac; however, if re-enabled by repeating the command with “enablelocal” as the final term, the problem may start up again.
With local snapshots disabled, you can still use your standard Time Machine drives normally to create and update your backups. The only difference is that Time Machine will require the presence of your backup drive to create backup versions of your files. For the most part, this will only cause a minor inconvenience if you want to access files that are automatically backed up by Time Machine. Otherwise, it will make no difference in how your Mac runs. You can also re-enable local snapshots at any time, if needed.