Time machine provides a great automatic backup for your entire computer, from which you can recover and restore individual files, folders, or even your entire hard drive. Once in while, though, Time Machine seems to slip through some sort of time warp and come out the other side leaving the current backup in the past and starting a whole new backup.
Mostly this occurs when you change hard drives, get a new computer or update OS X to a new version, but very occasionally it just happens.
Here is what your Time Machine backup drive looks like when it does. (Double-click your Time Machine drive on the desk top.) Only the second backup is actively being used. You can see the range of dates covered in each by clicking on the folder.
Unfortunately there isn’t a way to merge the backups into a single backup again. But it’s not a disaster; you can still browse and recover items from the earlier backup quite easily.
In the next window, you can choose the backup from which to browse and restore. This doesn’t change the backup set to which Time Machine currently backs up. It changes only the backup from which you can restore, and only temporarily. When you exit Time Machine, the default backup set returns to the currently active one.
Note that the Time Machine right-click menu item above was “…other Time Machine Disks…” Normally, you have only one Time Machine backup disk connected to your computer, but it’s possible to have more. For example, if for some reason I wanted to restore an old file that was on my wife’s Time Machine backup disk to my Mac, I could connect it to my Mac. Now choosing Browse other Time Machine Disks will bring up a window showing all Time Machine backups on any disk, including my wife’s which I just connected. You can also access backups from multiple machines stored on Time Capsule, or backups of multiple Macs on the same external disk.
So, it’s really pretty easy to get to your old backed up Time Machine data when Time Machine passes through a space-time wormhole and decides to start a new backup.
If you want to make accessing multiple Time Machine backups even easier, there is Back-In-Time 2 ($30, Demo version available). The biggest advantage is that it shows the combined contents of multiple backups in a single window (it doesn’t actually merge the backups). Some other capabilities:
- Show number of backed-up versions available
- Show version history of each item
- Show deleted items (date deleted and date of last backup)
- Drag and drop restore
- Access older backups on other disks
- Access backups from other Macs
- Calculate the space occupied by the backups
If you really access your Time Machine backups a lot, this might be pretty useful. For most people who only occasionally restore a file or folder from Time Machine, I think Time Machine’s easy built-in access to multiple backups (plus the new ability in Lion to access older versions of documents) is sufficient.