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I have a Dell XPS 15 (2013 model L521X - Windows 7) with a capacity of 680.3 GB on the C drive.

But WinDirSat says that 217.4 GB of that space is <Unknown> and I can't access it!  SpaceSniffer says that 215.8 GB is 'unaccessible space'!

The 'unknown' space is getting bigger by at least 1 GB a week – given the rate of increase, I think that this problem has existed since I got the laptop in 2013 or soon after. My laptop is now out of warranty and the explanation from Dell was laughable – they said that this amount of unusable space was normal!!

Has anyone experienced this – or know of any solution other than the ones I have already tried?

The 217 GB of Unknown space is definitely not system restore points. I have never set any restore points and have gone through the process to delete all restore points.

WinDirSat and SpaceSniffer don't list any files that are in this space – so there are no files I can delete. I have used CCleaner and the Windows Disk Cleanup to delete unnecessary system files.

I noticed that when clicking on the 'Cleanup System Files' button (in the Disk Cleanup), the progress dialog gets stuck on 'System error memory dump files' and then gives up. Perhaps there is some sort of logging or memory dump that is stored in an inaccessible directory

I don't have any other problems with the HD, RAM or Windows. Although I did have some problems when I first got the laptop with the Webcam not being correctly connected to the USB and got a couple of blue screens.

Scott - Слава Україні
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Stuart Haydn
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  • Some applications can trigger the creation of a restore point. Have you tried removing older system restore points via CCleaner? You can find them under Tools > System Restore. – VitaminYes Jan 23 '15 at 02:32
  • Could be alternate data streams https://en.wikipedia.org/wiki/Fork_(file_system)#Microsoft http://www.bleepingcomputer.com/tutorials/windows-alternate-data-streams/ Suggest checking with https://technet.microsoft.com/en-us/sysinternals/bb897440 with the command STREAMS -s C:\ – K7AAY Jan 23 '15 at 03:31
  • There are no restore points listed in CCleaner. I will check out data streams after work. – Stuart Haydn Jan 23 '15 at 11:00
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    Run TreeSizeFree as amdin (IMPORTANT) and post a picture here: http://www.jam-software.com/treesize_free/ – magicandre1981 Jan 23 '15 at 16:36
  • Might wanna try disk defrag. Not the most likely issue, but it is possible that your drive is horribly fragmented. – z7r1k3 Feb 04 '16 at 07:07
  • At the risk of insulting your intelligence — are you running CCleaner as administrator?  If you run it as your ordinary (unprivileged) user, it stupidly indicates that there are no System Restore points, rather than correctly diagnosing that it doesn’t have the privileges needed to see them. (That one confused me the first time I encountered it.) – Scott - Слава Україні Apr 24 '17 at 11:46

9 Answers9

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Most disk space management tools do not list alternate data streams, do not properly calculate hard-linked files and do not list the space in folders that you do not have access to, e.g. the folder "System volume information" folder in the drive's root. Without a tool that does all this correctly, you won't be able to get correct results for directory sizes. TreeSize Professional does this job once you activated the option "Track NTFS alternate data stream and hardlinks" in its options and have started it as administrator. Full disclosure: I am one of the developers of the TreeSize product family. A free 30 day trial is available.

In rare cases the structure on the volume may be damaged. in this case CHKDSK /F /SCAN /SPOTFIX might help.

In case the "System Volume Information" folder seem to be unreasonably large, you may reduce the space that Windows may use for shadow copies using this command: vssadmin resize shadowstorage /For=C: /On=C: /MaxSize=1GB. In this example, the space is set to 1 GB. As a quick solution you may execute this command: vssadmin Delete Shadows /For=C: /Oldest. It will delete the oldest shadow copies.

For both commands you need to run CMD.EXE as administrator.

Joachim Marder
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  • I have already checked Shadow copies, and there no space on my drive taken up by Shadow copies of files. I will check the other things mentioned later, thanks Stuart. – Stuart Haydn Jan 23 '15 at 11:03
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    This tool helped me to find that there is "System Volume Information" using a lot of space. – Radu Linu May 25 '20 at 09:36
  • In SpaceSniffer's configuration, there is also an option called "Scan Alternate Data Stream", but no avail for me even after enaling – Eric Wong Jul 31 '20 at 04:57
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    After using TreeSize and doing a comparison, turns out it was the OneDriver folder. Somehow SpaceSniffer skipped OneDrive entirely and became unknown, maybe synced folder has special data structure in NTFS? – Eric Wong Jul 31 '20 at 04:58
  • chkdsk X: /F /SCAN fixed my 1.7TB of UNKNOWN usage on a drive 50% unknown. – DarrenMB Apr 23 '22 at 15:58
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I had the same problem and read millions of pages explaning delete this that and those but none of them help me to find UNKNOWN files eating space in my disk.

In my case I found the solution by chance and it was easy, I hope ti may work for you.

  1. Right click on C drive (you may use the disk you need) and open properties
  2. There should be 2 options at the below ;first one is telling to compress disk and the second one is telling indexing filed and even contents of files please be sure you unchecked this option.
  3. Restart your computer.

As I said in my case this solved my problem but also be sure that you uninstalled programs like Dell Backup Recovery Tool too.

Let me explain why unchecking indexing solved my problem.I know indexing is a good thing but if you have 40gb Outlook PST file indexing is not helping you but just eating your free space.

I hope I could help you.

melic
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I'm currently running SpaceSniffer 1.3.0.2 on my Windows 10 and noticed the appearance of 4.4 GB of "Unaccessible space".

Running another instance as administrator revealed that that space is actually being used:

  • 2.0 GB in pagefile.sys, probably non-userspace swap.
  • 1.3 GB in "C:\Program Files\WindowsApps".
  • 1.2 GB in "C:\Windows", mostly "System32\config", "ServiceProfiles", "InfusedApps", and "System32\winevt" folders.

Also listed are:

  • 6.8 GB in "C:\System Volume Information".
  • 578.3 MB in "C:\ProgramData\Microsoft\Microsoft Antimalware".
  • 170.0 MB in "C:\ProgramData\Microsoft\Windows Defender\Scans".

The data in System Volume Information appears to be restore points and locked file buffers made by Volsnap; it's currently 0 bytes, which matches error 25 in the system log.

Cees Timmerman
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The first thing to check in this situation is just to make sure you're running your space usage scanner with admin privileges (right-click, Run as administrator).

Otherwise there's a good chance there will be system files that you can't access, and this unaccounted space will show up as Unknown.

mwfearnley
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Have you looked at your indexing, Windows.edb, file? A co-worker of mine had an issue similar to this where a large amount of disk space was being taken up why the Windows indexing service. We only found out about the issue after the user complained about running out of disk space.

Followed these instructions and deleted the file.

Miguel De Santiago
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  • Welcome to Super User! Can you reproduce the essential steps to delete the file in your answer here? :) – bertieb Apr 17 '18 at 09:30
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In case of "System Volume Information" you can use the following to cleanup.

  1. Open an elevated command prompt.
  2. In the elevated command prompt, type wmic and press Enter. After a few seconds wmic:root\cli> will appear.
  3. Type the command shadowcopy delete and press enter.
  4. You will now be asked Y/N for if you wanted to delete the available shadow copies one by one. Type your answer and press Enter after each one.

After this process you can type vssadmin list shadowstorage in order to see the allocated space and also that the storage was erased.

Radu Linu
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this is a 2022 update,

  • SpaceSniffer 1.3.0.2 is on Win10 unable to read 300+GB of "Unaccessible space". OneDrive contents reported in only few GB range.
  • WinDirStat 1.1.2.80 is able to discover the above space as files in my personal and work OneDrive, over 200+GB as of now and still scanning after 4minutes.
  • WizTree 4.10 does an initial scan just under 7secs reporting 271+GB used by OneDrive.

I guess the newer tools and versions are reporting much more accurately and quickly.

steo
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  • Your answer could be improved with additional supporting information. Please [edit] to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers [in the help center](/help/how-to-answer). – Community Sep 25 '22 at 09:24
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From a command prompt, run chkdsk /f repeatedly until there are no errors (you may need to reboot if it's a system drive).

As recommended in the comments, check for restore point usage.

Next, many applications don't see space used in hidden and/or system folders, and many programs (antivirus, for example) store stuff in those folders, so you may need to run dir /ash to get a list of system and hidden folders followed by dir <foldername> /ash /s to find out how much space the folder using (you may need to drill down into it to find the offending files).

James
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  • I have run chkdsk a couple of times and after each time the Unknown space increased considerably! So I will try other stuff in these answers first. – Stuart Haydn Jan 23 '15 at 10:59
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In my case the problem was offline files. I work for a large corporation and we had several multiuser windows 7 clients. The problem was the synchronization of "MyDocuments". When 10 users synchronized these folders we ended up with 50+ Gb in C:\windows\CSC and his space does not show easily. You have to take ownership of many folders but if you do the numbers make sense. I am trying to reinitialize the cache but it seems we have GPOs which determine this behaviour. Again makes sense for single user clients but not for multi user.

So , look for hidden system files. Would be nice if there was a tool, which could show them.

JEA
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