How to Fix a Mac with “PB” Disk Space

Is Finder (or even Disk Utility) reporting PBs worth of data being available? Here’s the fix.

So annoying. This can be due to a number of things, but the single most common – particularly if you’re running OS X 10.10 (Yosemite) – is related to Time Machine. The long story short is that by default, your Mac creates “temporary” backups for Time Machine, and these are stored in a hidden folder on your primary drive called .MobileBackups

This folder can only be accessed or even viewed if you ‘raise your user permissions’ to root (if that doesn’t make sense, don’t worry).

Here’s how to fix the problem, and instructions on how to stop OS X from even creating the temporary backups in the first place (at the end of the tutorial) – if you’d like.

  1. First things first, run a Time Machine backup. If you have to wait because your Time Machine drive isn’t handy, do so. Since this tutorial involves deleting files, it is critical that you have a backup in case something goes wrong. If you want to proceed without running a backup, do so at your own risk.
  2. I use an absolutely fantastic (and free) App named “Disk Inventory X” to determine which files and folders are taking up the most space on my Mac – especially when working on my MacBook Air, which has a fairly small hard drive.

    Even using that program, I was unable to figure out why on earth my Mac was reporting “PBs” worth of available disk space. It wasn’t until I used Disk Inventory X as the “root” user that I saw where all the space had gone – into a folder name .MobileBackups. See the screenshot below (may need to click it to view properly).

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  4. Inside of that .MobileBackups folder were a slew of files I had long since deleted. Many of which were also already backed up in Time Machine. As illustrated in the screenshot below, I even had a 9.8GB file hiding in there.
  5. Not only are there a whole bunch of useless files taking up space on your drive, but it’s causing OS X to become confused as to exactly how much space is available. To solve the problem, you have to manually delete the files via the “command line”. It’s not that complicated. Start out by navigating to Applications -> Utilities and launch Terminal.

    Copy and paste the following command into the Terminal window, and hit Enter. You’ll be prompted to enter your password. Do so, then hit Enter again.

    sudo /Applications/Utilities/

  6. click to enlarge

  7. Another (separate) Terminal window will open up. This one will have root# in front of the cursor. Now enter the following two commands, one after the other.

    cd /.MobileBackups/

    rm -rf *

  8. click to enlarge

  9. Now you can close all of the open Terminal windows. You may need to log out and back in again (or just restart your Mac) – but Finder (and the rest of OS X) will now recognize the proper amount of disk space used and/or available.

  10. click to enlarge

  11. If you would like OS X to stop creating these temporary backups completely – open a Terminal again, and enter the command:

    sudo tmutil disablelocal

    If you’re prompted for your password, enter it.

    You’ll need to re-run that command each time you update Yosemite from version to version (eg. 10.10.2 to 10.10.3 etc) – as OS X will re-enable the temporary backups each time it’s updated.

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2 thoughts on “How to Fix a Mac with “PB” Disk Space”

  1. Thanks! This helped me. I had 141 TB of available space. If only this were true! Wouldn’t you just love to have 2.25 PB of free space? That would be a real dream come true!

    P.S. I did this by booting from the recovery drive and using the Terminal there from the Utility menu as that is running in root by default.

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