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I have a 13-inch MacBook Air, and have been using it for about a year now. There are 23.6 GB of memory that appear to be missing from my hard drive. About This Mac -> Storage shows 91GB of files, of which 61GB are "Other": I can account for the files that are not under "Other".

The command df -h agrees, showing 91GB used (command output shown below):

    Homes-MacBook-Air:~ BrandonWork$ df -h
Filesystem      Size   Used  Avail Capacity  iused   ifree %iused      Mounted on
/dev/disk1     112Gi   91Gi   21Gi    82% 23864730 5456996   81%   /
devfs          188Ki  188Ki    0Bi   100%      651       0  100%   /dev
map -hosts       0Bi    0Bi    0Bi   100%        0       0  100%   /net
map auto_home    0Bi    0Bi    0Bi   100%        0       0  100%   /home
/dev/disk0s3   620Mi  548Mi   72Mi    89%   140256   18434   88%       /Volumes/Recovery HD
/dev/disk3s2    16Mi  9.8Mi  6.2Mi    62%     2503    1581   61%       /Volumes/Disk Inventory X

However, here the problem arises, as when I examine the disk, only 67.4GB are actually used: What the hell?

I have six user accounts on this laptop due to my family borrowing it repeatedly, and have run Disk Inventory X on all of them, as I was told that other users' files could account for it, as they are not visible to non-admins. None of them had more than 2GB of files. I have also used OmniDisk Sweeper, with similar results. I have seen all of the following possible problems and solutions, to no avail:

  1. Swap files (they are seen by Disk Inventory X)
  2. Temporary caches (restart your computer; didn't help)
  3. False volumes in /volumes (checked; don't have anything weird there)
  4. Viruses (multiple scans with different programs turn up nothing)

On a previous computer, I had a similar problem with eaten memory; turned out to be WinRAR generating huge .txt files, and these could be found with Disk Inventory X.

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    If you run a command like sudo du -sm /Users/* that will let you know all the allocations on user home folders. You can run that from Recovery HD to avoid false reporting or external mounts - but that's an oddball situation. Are you averse to using a tool like DaisyDisk that can run as administrator / root so that you can get a better picture with one scan than needing to juggle 6 runs of the program you are using – bmike Apr 24 '16 at 15:11
  • The "About this Mac" storage summary is somewhat unreliable. It always show weird figures. – Max Ried Apr 24 '16 at 18:32
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Both About this Mac and df seem to agree that you have 91GiB used, 21GiB free on /, which adds up to the volume of your 112GiB (120GB) hard drive.

The problem must be with the list of files Disk Inventory X scans.

Run du -s as a superuser starting from / and then going deeper into the filesystem to get a more accurate picture of your disk space usage.


Keep in mind:
About this Mac and Finder display space in GB (base 10, 1GB = 1000MB)
df -h and du -h show results in GiB (base 2, 1GiB = 1024MiB)
df -H and du -H show results in GB
Many GUI tools display file size in GiB while labeling it as GB

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Half a year later, turns out this was a known issue with OS X Yosemite and Spotlight indexing. Upgrading to Sierra fixed it.

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