Losing hard drive space to 'Backups?' Don't panic!

Apple's Time Machine software makes sure that your Mac is always backed up, either to a Time Capsule device on your network or to an external hard drive. One of the lesser-known functions of Time Machine is its ability to save "snapshots," which can grab big chunks of your hard drive. If you've had this happen to you, don't worry — everything's going to be okay.

You click on the menu then select About This Mac and click on the Storage tab to check on how much space your hard drive has available. Then it hits you: There's a huge swatch of color dedicated to "Backups." What's going on?

Time Machine backups

First of all, let me assure you: If you see space on your hard drive dedicated to backups, nothing is wrong. In fact, Time Machine is working exactly as it's supposed to.

Under ordinary circumstances, Time Machine backs up periodically whenever it knows that its Time Capsule is on the network, or when the external hard drive it uses for backups is connected. It backs up hourly for the past 24 hours. It keeps daily backups for the past month. And it keeps weekly backups for all previous months, within the storage limit of your target drive.

This means you can always restore your hard drive to how it was right before a catastrophic failure, like dumping a can of Coke on your laptop or dropping your MacBook Air six feet on hard pavement and watching it crack like an egg. But these periodic updates also allow you to recover individual files you may have deleted, which you might need again.

Of course, all this assumes that your Mac has continuous access to that backup hard drive or your Time Capsule. And that's a pretty big assumption. Maybe you bring your Mac to work, or to a friend's house, or to the coffee shop. Maybe you've left that backup hard drive disconnected for a few days. Or weeks. Or months.

Time Machine doesn't arbitrarily stop working just because it can't find the backup drive. Instead, it creates local snapshots on your computer. These snapshots are what Apple calls a "safety net" for when your normal backup drive isn't around. If you accidentally delete a file, you can still recover that file using the local snapshot instead of the backed up content. When you activate Time Machine, you'll see those local snapshots distinguished with pink tickmarks, instead of grey ones.

Time Machine keeps track of how much your hard drive is being used, and if there's less than 20 percent of the drive available, it'll start to delete snapshots starting with the oldest. And if you have less space than that, Time Machine gradually gets more aggressive about removing snapshots itself.

So ordinarily, you really don't have to worry about how much space Time Machine might be using for snapshots — it'll take care of the housekeeping itself.

I strongly recommend you let Time Machine do its thing. After all, these snapshots are disposable. In fact, if you compare the amount of disk space that About This Mac says is used to a Get Info command from the Finder, you'll see there's a difference. Because the Finder considers Time Machine snapshots as disposable, and doesn't count them.

If you're really freaked out about Time Machine snapshots grabbing hard drive space, though, you can shut Time Machine off — temporarily — and that'll fix it.

First of all, let Time Machine sync with the backup hard drive or Time Capsule, so you'll have the latest backup to restore from if anything goes wrong. Once that's done, eject or unmount the backup drive, if necessary. Then do this:

  1. Click on the menu.
  2. Select System Preferences....
  3. Click on Time Machine.
  4. Toggle Time Machine from On to Off.
  5. Close the Time Machine window.

Time Machine preferences

Time Machine backups off

That's it, that's all you need to do. Restart your Mac to refresh that storage usage map you see in About This Mac, if you want to. All the snapshots will have gone away, and "Backups" won't have grabbed a big chunk of your drive.

Time Machine backups after

You haven't lost anything: All of that data was backed up on your last Time Machine archive, which you should have done right before turning Time Machine off.

Once you're ready to resume business as usual, just open up Time Machine again and toggle it back on.

Any questions?

Again, this sort of thing is the Mac working exactly as it's supposed to. I really wouldn't recommend messing around with Time Machine once you have it set up — it's there to protect your data, and your Mac will take care of whatever it needs to if the local snapshots get too big.

Having said that, I've had a few customers come in confused about this, so I figure it's worth pointing out.

This is pretty straightforward, but if you have any questions about how Time Machine works or anything I might have left out, let me know.