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I recently noticed that one of my external hard drive seems to be missing a lot of space. It was recommended that I try WinDirStat, as it could help identify how much space each file was taking up. This is the result:

http://i.imgur.com/KU0Yia7.png

As you can see, there is about 244.7GB "unknown" usage.

Doing a bit of research online, the most common suggestion was (a) Recycle Bin and (b) System Volume Information.

(a) As you can see, empty. To double check, I ran Disk Cleanup. It confirmed that it was empty. (Note that a new file appeared by the time I took this screenshot, but it's only 129 Bytes.)

(b) Harder to tell. However, according to various forums, the most common reason for System Volume Information to grow large is due to System Restore Files. I had a look, and it is definitely turned off for this drive, as seen here:

http://i.imgur.com/JZ49qrC.png

What else could be causing this issue? It is an enormous amount of storage to have gone missing!

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  • "System Restore Files. I had a look, and it is definitely turned off for this drive" - was it ever turned on in the past?
    – DavidPostill ♦
    Commented Aug 30, 2015 at 10:23
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    Did your run windirstat as administrator?
    – DavidPostill ♦
    Commented Aug 30, 2015 at 10:28
  • @DavidPostill This is the first time I've checked system protection settings since buying the drive earlier this year, so I'd say that it has never been turned on. And yes, this was run as administrator.
    – BSnapZ
    Commented Aug 30, 2015 at 10:53
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    I prefer TreeSizeFree over WinDirStat . Run TreeSizeFree as admin to see more.
    – magicandre1981
    Commented Aug 30, 2015 at 18:22
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    @magicandre1981 I just took your advice and tried using TreeSizeFree. It actually did find the missing space! It is a very well hidden folder which I can only assume was created by the backup software I use (CrashPlan). Now I just need to figure out whether it needs to be kept or not... i.imgur.com/JE6fVzt.png
    – BSnapZ
    Commented Aug 31, 2015 at 6:11

6 Answers 6

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Instead of windirstat you should use TreeSizeFree.

enter image description here

Run it as admin, so that TreeSizeFree shows all hidden/system files.

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    Thanks. In my case, it showed that the <unknown> space of 40 GB was the virtual drive used for Docker (C:\Users\Public\Documents\Hyper-V\Virtual hard disks\MobyLinuxVM.vhdx).
    – Michaël Polla
    Commented Nov 5, 2017 at 14:54
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    I don't see how TreeSize can help. I have an <unknown> of 100.6 GB on the C-drive (reported by WinDirStat) and TreeSizeFree reports a Size of 54.2 GB and 54.3 GB Allocated on C-drive. The total size of the C-drive is 213 GB.
    – AH.
    Commented Oct 21, 2019 at 9:05
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    you need to run it as admin...
    – magicandre1981
    Commented Oct 21, 2019 at 14:40
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    I tried TreeSize and it cannot free "unknown" space for instance allocated by multiple restore points.
    – AH.
    Commented Oct 31, 2019 at 8:58
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    Run WinDirStat as admin and you will also see what occupies previously unknown space. No need to install yet another program.
    – Monsignor
    Commented Aug 8, 2022 at 5:24
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Running Windirstat as Administrator will reveal most of this. In some cases it can be system protection files, corrupt files, old installers, or in my case, the Recycle Bin.

Per the Windirstat Propaganda Blog,

https://blog.windirstat.net/20061013/unknown-space/

This mysterious item is just the difference between what Windows reports as the free space on the volume minus size of the files WDS can access. Please note the part WDS can access! This is the important point here. WDS cannot access the files under System Volume Information on all the (NTFS?) drives, so it cannot sum up the sizes of these items. And by the way, we have had reports of up to 30 GB of “” space.

The root of the problem is permissions, apparently.

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    Thanks, run as administrator brought my WinDirStat <Unknown> space from gigabytes to zero.
    – Bob Stein
    Commented Jul 29, 2020 at 12:54
  • Yep, no need for different software, just run as admin. Turned out to be a game installed via the Xbox app in my case.
    – Matt Lacey
    Commented Apr 27, 2021 at 23:13
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In my case it's the Windows search file, Windows.edb, in: \ProgramData\Microsoft\Search\Data\Applications\Windows.

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    Can you please elaborate a bit more for what the file is and how much it takes up for other future answer seekers?
    – Eric F
    Commented Apr 9, 2019 at 19:12
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This might be of interest, or not.

I run WinDirStat (NOT as admin) and get 7.3GB unknown. Program Files 1.7GB. When I run it as admin I get 5.2 and 3.2GB respectively. There are other differences too but I won't muddy the water by posting all of them.

It's definitely a permissions issue for me. For example the difference in Program files is the WindowsApps directory. I changed the owner from Unable to display... to ....\users and WinDirStat sees it in either mode (no admin/admin).

Same for SystemVolumeInformation, despite not being able to change owner for all items. Found all but 0.6GB of unknown space. Some of the remainder is in ProgramData and small amounts in other places e.g. Config.Msi.

I am not so concerned as to spend time hunting through the whole drive and changing premissions but I now understand the differences. Hope this helps.

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For others facing this same question, you might want to check the VSS settings to be sure the amount reserved for shadow copies is not consuming too much space. (ie right click the drive in windows explorer and choose "Configure Shadow Copies")

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    – Community Bot
    Commented Oct 24, 2022 at 19:33
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Important to know is how WinDirStat works and what this "unknown" means. For example: you have a drive of 256GB. You run WinDirStat and it will scan all the files it has access to. Let's say you run it as a normal user. That user has no permissions to 'see' all the files. If the list WinDirStat can see as that user can see 200GB, there will be 56GB unknown. It is logical that the administrator can see more files compared to a normal user. There are situations where the administrator still could only see a limited amount of GB's.

For example:

  • Previous versions of files
  • Shadow copies
  • Filesystem errors (ex: not reclaimed free space - run "chkdsk c: /F" and reboot to fix this)
  • ...
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  • Avoid posting answers to old questions that already have well received answers unless you have something substantial and new to add.
    – Toto
    Commented Feb 9, 2023 at 12:24

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