MobileBackups not being backed up
It has been my experience (with a non-full SSD in a MBA running 10.8.2) that the /.MobileBackups directory always holds hourly backups from the last day and daily backups from the previous seven days. These are kept locally (even after making a Time Machine backup to an external disk) so that you can still use Time Machine to restore recently changed files even when your external Time Machine disk is not available.

Accordingly, it makes sense that your /.MobileBackups would be large if you have made correspondingly large changes in the past week (i.e. deleted or changed big chunks of data).

I have not yet filled my disk, so I am not sure how it works in that situation. Ideally, it would “give back” some of the space /.MobileBackups earlier than normal instead of letting you completely fill up your disk.



If you are not critically short on “disk” space, you can probably just wait a week or so (while doing daily backups to an external Time Machine disk) and /.MobileBackups should automatically shrink as the locally stored data ages (assuming you are not still making “large changes”).

If you need the space (and Time Machine is not automatically giving it back as the disk gets full), or you need to constantly make “large changes”, then you can try this command (in a Terminal window):

sudo tmutil disablelocal


I have never run this command; the manpage has this description for disablelocal:


  Turn off local Time Machine snapshots and trigger automatic
               cleanup of accumulated local snapshot data.