I have a RAID 5 solution with 4 disks of 2TB. That gives me 6TB disk space. Now Disk Utility tells me that my actual usage is 3,5TB and I have 2.5TB free space. But when I add up the disk usage of the individual folders then this does add up to 2TB. So there is a gap of 1.5TB.

I have deleted a very large folder recently. Could that explain it ? That disk utility is not reporting the actual situation ?

EDIT: I have downloaded OmniDiskSweeper and this app gives this list of my disk group:

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So my folders add up to 2.0TB. Here is the disk info that my MAC gives me:

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As far as I can tell I see a difference of 1.5TB. I am no techie so I cannot explain this.

  • 1) Your gap is .5TB, not 1.5TB. 2) That's possible. I was working on an iMac recently with a 1TB drive. Between "About this Mac" and the actual folder storage there was a discrepancy of >200GB (more than 20% of the entire drive space). I wouldn't worry about it too much unless you're running out of room and absolutely need to know whether those 500GB are available, but it looks like you've got a while (2TB) until then. – NoahL May 11 '17 at 15:19
  • My actual Disk Usage as reported by Disk Utility is 3.5TB and when I add up the disk usage of the visible folders then it is 2.0TB ...so this is a difference of 1.5TB. – Old Man May 15 '17 at 9:48
  • "when you add up the disk usage of visible folders...." How did you calculate this? How did you account for hidden files/folders? Please provide the output from the command df -h by editing your original question and adding the details. – Allan May 15 '17 at 10:21
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    And any visual folder method won't account for trashes – NoahL May 15 '17 at 17:34

First of all, empty your trash, reboot & try out disk utility again if you haven't already. If that doesn't do it though you'll have to dig a bit more.

Here's the terminal command for finding hidden files & folders: defaults write com.apple.finder AppleShowAllFiles YES. Put sudo in front of that if it doesn't work - you'll have to enter your user password in this case. Once you've done this restart finder by clicking the apple icon in the menu bar and heading into 'Force Quit...'.

Now if you open Finder, select 'Go' & 'Computer' from the menu bar, go into the drive in question. I would put this into 'list' view and make sure that the size option is on. For any folders that aren't showing their size, highlight them (hold command + click to select multiple) and then hit command + i to pull up the Get Info menu for them. You'll see that under the size field they're 'Calculating Size'. Just keep those windows up & wait for them to finish - for the sizes you're dealing with this could take potentially hours. Add them up again & see if the size is accounted for.

If there's still 500gb or so missing I would recommend to backup & reinstall OS X. You can select only exactly what you want to using Time Machine, see the size before you even finish backing up, and then restore.

  • The Raid 5 is an external disk group. – Old Man May 17 '17 at 8:40
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    Doesn't matter - this all still applies. – little tiny man May 17 '17 at 15:45

Part of the issue is that there are different methods to calculate space. I would first run Disk Utility on the RAID array to ensure that the file system structures are good (if they're not, you can get incorrect free space readings), then run OmniDiskSweeper (https://www.omnigroup.com/download/latest/OmniDiskSweeper) on the volume and check again.

  • I have made an edit in my question – Old Man May 17 '17 at 8:39

To find out about your actual disc usage by-folder, open a Terminal (Applications->Utilities->Terminal) and enter the following command

cd /; du -cgd 1 . 2>/dev/null

The output will be a list of folder sizes (in GB) like this

1   ./_CO2
8   ./_film
3   ./_ins
23  total

If this does not add up, try

cd /; sudo du -cgd 1 . 2>/dev/null

and give your root password.

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