One of the nice new features of OS X Lion is that you can access your Time Machine backups even when you are disconnected from the drive such as on the commute to work or even while on holiday. The downside is it takes up a chunk of your HD that you might not want to give up. Fortunately, you can turn this feature on or off (it’s on by default in Macbook’s, but off by default in iMac/Mac Pro).
When the feature is on, local snapshots of the last few days’ Time Machine backups are stored on a local drive called MobileBackups. If your time machine backup disc should get corrupted for any reason, these can also serve as a second line of defence. Be careful though, these backups get replaced and updated without warning, so don’t rely on them for anything more than the last couple of days saves.
You can access these from the regular Time Machine icon. Alternatively, find them by clicking on the computer name at the bottom of the left-hand column in any Finder window, and then navigating to the MobileBackups drive.
If you want this option on your iMac/Mac Pro, you’ll have to enable it through Terminal. Open the Terminal application and paste in the following command:
sudo tmutil enablelocal
followed by your admin password and a return-key stroke (don’t expect to see anything when you type the password).
If Terminal returns to the prompt you should be good to go. Check by opening Time Machine preferences, which should now display the message that “Time machine keeps local snapshots as space permits and…” followed by the Time Machine backup schedule. If it hasn’t worked, it’ll just say “Time machine keeps:” and then the schedule.
If you wish to disable local snapshots to save disk space (mine takes up about 8GB), then just type:
sudo tmutil disablelocal
Since OS X Lion is only available via download from the App store, you may be wondering what to do if you need to recover the whole OS. In times past, you’d simply insert the original CD/DVD that the OS came on, but how do you do this if the OS is download only?
Apple has provided a couple of different ways of effecting a full recovery of Lion. In most cases, so long as you are connected to the internet either by Wifi or ethernet cable, you can simply restart your machine while holding down the Command key and the ‘R’ key on the keyboard (Cmd-R).
This will put your machine in recovery mode, and you can follow the instructions from the start up screen. Initially, your machine will try to recover from a special Recovery partition that Lion created on your hard disc when you originally installed it. However, if your HD is corrupted or unavailable for some reason, Lion will attempt to recover the OS directly from Apple’s servers. In cases, be aware that you need an internet connection.
If Lion cannot re-install on your internal disc, or if you want to move the OS to a new or external disc, you will need to go through a few preparation steps. To learn about these and more about Lion’s recovery options, see the full Apple support article here.