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I have 250 GB of hidden space which I cannot track down. I've tried deleting it on Daisy Disk as an admin but I couldn't delete it. I don't know why it's happening but all I remember is using rEFIt and creating a partition a couple of months ago. I do remember deleting the partition and it was alright until now. screenshot of memory usage

DaisyDisk

  • Are you using the sandboxed version of the program from the App Store or the downloaded version? My guess is the files aren't really hidden - just that your user (or the sandboxed app) can't really get into the directories where those "other" files are stored. – bmike Sep 8 '13 at 15:26
  • Can you upload an image of the partition mapping using disk utility? – Samantha Catania Sep 12 '13 at 6:26
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My guess is the software did subtraction to show you the value of "hidden space" and the only thing going on is that the operating system user that ran the tool doesn't have read permission in some directories where files are stored and cannot show you a breakdown of those files. Basically, it added up all the files it could count, totaled their size (161.5 GB), noticed that the disk says there is only 86.85 GB free and told you that the balance of 250.8 GB was hidden space.

You can test this by opening terminal and pasting this one command:

du -sg /Users/*

This tells the system to calculate the disk usage in gigabytes of each user folder (and the shared folder). This is part of the way that the system protects one users files from being read by another user. Watch for errors showing places you do not have read permission.

You can also see this effect in finder by turning on View -> Show View Options and clicking "Calculate all sizes"

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I have three users on this computer and when I use Finder or the program What Size (it shares some common functionality with Daisy Disk and also has a version on the app store as well as a more powerful version that ships separately) the normal measurement cannot see in folders where my "user" has no permission to go.

enter image description here

When I toggle the measurement as a user or as the admin / you can see in the second screen that the accounts starting with a and r have at least 250 folders and about 1000 files each. In this case, they don't occupy much space, but in your case, 250 GB of files are stored in locations where your tool cannot measure them.

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Hopefully this helps explain why the tool is showing you hidden files. If you have multiple users on that Mac, perhaps running the tool once for each and looking in the /Users folder, you can locate where the space is being used. If you do not have multiple user accounts, you will have to see if Daisy Disk has the ability to run in admin mode or use the terminal to calculate disk usage where you can run the command as the "root user" by adding a sudo and typing your account's password to let the system grant access to those normally non-readable files.

Mac:~ me$ sudo du -sg /Users/*
Password:
39  /Users/Shared
1   /Users/aaa
132 /Users/mmm
1   /Users/rrr
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Try starting up from the recovery partition and repairing the main OS X volume (like Macintosh HD, indented below a drive) from Disk Utility.

I had a similar problem, but there was only about 25 GB of disk space classified as "hidden space" by DaisyDisk. When I used Disk Utility to verify the Macintosh HD volume, there was an error about an invalid free block count, but I was able to get rid of the error and free up the hidden space by repairing the volume from the recovery partition.

  • That would be quite the find - recovering that much space from a fsck - even 25 GB is a lot of slack to lose track of. Great idea to check this. – bmike Sep 9 '13 at 0:46

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