Local snapshots for Time Machine is one of the new features in OS X Lion that looks really good on paper. But once you have used your new Lion installation for a few days, you will notice that you are running out of disk space. After some digging around I noticed that the /.MobileBackups folder that is used by Time Machine for local snapshots was at nearly 50GiB, even though the external Time Machine backup disk was connected most of the time. I guess this is done to speedup Time Machine in the common case, and make backups available when not connected to the external Time Machine disk.

Besides the disk space issue, the local snapshots feature also slows down your MBP noticably. You’ll notice that the disk is spinning most of the time, and the file copying performed by Time Machine trashes your caches. Everything feels terribly slow after some time. Thankfully Apple engineers included a switch to turn of the local snapshots feature, tmutil supports a new command disablelocal in OS X Lion. Use the following command to disable the local snapshots feature of Time Machine:

$ sudo tmutil disablelocal

Note that it might take some time for Time Machine to cleanup the /.MobileBackups folder.