I had this problem a few weeks ago where my C: drive would fill up over night. When I came to work in the morning my drive would be full, after reboot I'd about 200GB free. I tried cleaning up with disk clean but that didn't free enough up, then I looked at winDirStat and it only show 300GB of space being used. After getting super confused I found out how to display the "unknown" file type and found that was filling all of the free space. After a lot of duck(and google)-fu I found about the storage sense and cleared up the storage issue.

Today I get a notice from backblaze that my disk space is low, and sure enough these unknown files are back, but this time StorageSense isn't removing them. so I'm sitting on 101GB of spacing being used by non-file objects.

Sorry for the novel, TLDR:

  1. Drive was full
  2. Windirstat(as admin) shows 200 gigs not used by files, taken up by unknown
  3. Cleaned unknown space hogs with StorageSense, stopped being and issue
  4. Wait couple weeks
  5. free space is fill again with unknown data
  6. StorageSense isn't cleaning

WinDirStat Updated WinDirStat

  • 1
    I went ahead and closed this as a duplicate, since the duplicate question asks the same question, and the answer is highly upvoted. If you want a solution to the disk usage, you can simply edit the question, and provide a different screenshot indicating what the 100 GB files worth of unknown space actually is. Anyone with a gold badge on the Windows 10 tag can instantly reopen it (easier to do it this way in the event you can solve the problem yourself). You can also run WinDirStat as an Administrator.
    – Ramhound
    Mar 23, 2021 at 23:06
  • @Ramhound I would love to show what the 100GB of unknown space is, but I can't find out, neither windirstat, not TreeSize report it even when run as administrator
    – Apeiron
    Mar 23, 2021 at 23:15
  • When you refer to Storage Sense, have you also ran the Disk Cleanup tool? They have slightly different functionality. Additionally, what about your System Restore Files, what is your current settings? Your screenshot doesn't list all your files on the disk, if you shrank the graphical element, all the files could easily be shown. Personally, I have had more luck with WizTree, approaches listing files a little differently
    – Ramhound
    Mar 23, 2021 at 23:18
  • I did run the disk cleanup, there were a lot in recycling to remove, ~60 GB and I removed a 40GB hyper-V image which is why there was 100GB of free space. system restore was disabled, but I enabled it and it's set to 2%, 10GB. Thank you for the help so far, I will have a look again when I get back to work tomorrow.
    – Apeiron
    Mar 24, 2021 at 0:38
  • So I came in this morning, my hard drive is full again, I tried StorageSense cleanup, it freed up <1MB. I rebooted and now I ahve ~225GB free. Is it possible there are some folder with bad permissions ?
    – Apeiron
    Mar 24, 2021 at 16:13


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