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My disk space usage doesn't add up. I should have used only about 80 gigabytes, but according to DaisyDisk about 25 gigabytes is taken up by hidden space. The mystery disk space seems to be classified as other in the About This Mac window.

I've disabled local Time Machine snapshots with sudo tmutil disablelocal and deleted /Volumes/MobileBackups/.

Does anyone know what the hidden space could be or how I could free it up?

Possibly related to Macbook HD "Other" all the Sudden Almost Full.

  • How many users do you have? DaisyDisk might be unable to access a different user's directory. – Vlad Mar 21 '12 at 9:13
  • @Vlad Just one. And the DaisyDisk (and du) results in the screenshot were scanned as root. – Lri Mar 21 '12 at 9:17
  • What does df -h output? – Vlad Mar 21 '12 at 9:22
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    Reboot into Recovery HD and run a disk repair in that environment. Sometimes there is corruption in the volume of the file system. That should fix it or at least identify any problems if they exist beyond just having content taking up space unnecessarily. – user10355 Mar 21 '12 at 9:31
  • Restarting may resolve the problem. I had 20GB of hidden space. Following user10355 and user495470, I ran DiskUtility first aid, first without restarting (i.e., on the boot partition while booted from the boot partition), and then in recovery mode (i.e., on the boot partition while booted from the recovery partition); both methods reported no errors. But after restarting again from the boot partition like normal, the hidden space was down to 1GB. YMMV. – Jess Riedel Dec 28 '18 at 16:39
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Starting up from the recovery partition and repairing the disk fixed the issue. (Disk Utility showed an error about an invalid free block count.) Thanks @cksum.

  • From what I can tell reading the documentation and running the program on several different machines is that the hidden space captures storage inefficiencies by subtracting the expected space from each allocation that was measured and providing the difference as "hidden space". I wonder if your unallocated block counts were the cause or if it was more severe catalog and filesystem corruption to make 25 GB "go missing" – bmike May 14 '14 at 17:08
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Another possibility—and one that ended up being the culprit in my particular case—is that your machine is making local backups when it's unable to connect to your external backup source. In this case, you can just disable the backups by entering the following command in the Terminal:

sudo tmutil disablelocal

Later, if and when you decide to re-enable the backup, you can reverse it with the following Terminal command:

sudo tmutil enablelocal


Update for MacOS Sierra and Later

It seems like the disablelocal and enablelocal commands are no longer available. As an alternative you can delete local snapshots by doing the following:

  1. Get a list of the local snapshots by running:

    tmutil listlocalsnapshots

    You should get some output like

    com.apple.TimeMachine.2018-10-03-145245.

  2. Delete a snapshot by running:

    tmutil deletelocalsnapshots <date of snapshot>

    So, for example, using the output from step 1, you would run:

    tmutil deletelocalsnapshots 2018-10-03-145245

    And you should get some output like

    Deleted local snapshot '2018-10-03-145245'

  • Thanks for these tips. I had the same problem, with 350 GB (which I just deleted in DaisyDisk) not showing up as available again. First, I repaired the root volume (in recovery mode), then I used sudo tmutil disablelocal (and rebooted), but I also had to start another time machine backup (to an external, USB-connected disk) until the "used space" would finally drop from 411 GB to 62! – hans_meine Dec 31 '14 at 10:58
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    Just FYI for people who come across this: it seems the disablelocal command does not appear to exist in tmutil in High Sierra. I don't know what the replacement is. – mhucka Apr 14 '18 at 18:48
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DaisyDisk's hidden space (if scanned as administrator) should be within 4-8GB limit for most Macs. If the numbers are larger, try repairing the volume as this may serve an indicator for file system errors.

Taras Brizitsky, DaisyDisk's designer.

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    Welcome to the site. Feel free to add your information to your profile and thanks for self-disclosing your relationship to the product as that is encouraged to provide transparency in case of recommendations, etc... – bmike May 14 '14 at 17:05
2

According to DaisyDisk manual:

Sometimes the amount of "used" space on a disk may appear greater than the total size of all scanned files and folders on that disk. This is normal. The difference is usually taken by the file system overhead and system stuff like Spotlight index, but in certain cases a significant amount of disk space may be hiding in other users' accounts or folders that are normally not visible to you. In order to reveal those folders you should scan the disk as administrator.

(Hidden space) is a virtual disk map item that only appears when the total size of restricted files is significant, so you can see whether it's worth rescanning the disk as administrator or not.

Large amounts of hidden disk space may also indicate to file system errors. Follow our troubleshooting guide for details.

In case you have a lot of hidden disk space when running it as administrator, it's possible that you have file system errors or broken file permissions.

0

I noticed this folder /.MobileBackups.trash was taking a lot of space (62GB!). Check yours with sudo du -hs /.MobileBackups.trash

Just ran sudo rm -rf /.MobileBackups.trash and got my space back.

0

In my case I was missing 771 Gigs of space. I had to clear my /cores folder. Apparently an application was crashing and leaving core dumps the amount of space missing was the exact amount of disk space in the cores folder.

0

Another possible culprit could be homebrew (if you are using it). By default, it keeps old vesions of the installed packages after updates. In my case, this summed up to ~11GB. Run brew cleanup -n to see how much space these backups take up on your machine (this won't delete anything yet. To do so, leave out the -n flag).

Source: https://til.hashrocket.com/posts/44a4b95cdd-homebrew-is-eating-up-your-harddrive

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