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Something is "eating up" storage on my C: drive recently. It's a 107 GB drive; a few days ago size of "All in c:" showed up in properties as ~ 67 GB (size on disk was LESS though I cannot recall ever making compressed drives) with very little free space. I used disk cleanup, removed everything it suggested, plus moved ESD and Hotfix folders to a different drive, removed ~ 15-20 GB of unnecessary apps, disabled hibernation, stopped windows update service etc. but the drive keeps filling up.

Yesterday (last effort) e.g. I freed ~ 10 GB, and this morning all is gone, 48GB used / 39 GB on disk, 0 free space! The computer is always on, it's an office machine to which I connect via remote desktop from home.

Any ideas what I could do to reverse this madness short of reinstalling Windows?

EDIT:

Downloaded and ran SpaceSniffer based on commenters' advice. Ran as administrator, turned on all options to scan/detect everything. It shows 55 GB as Inaccessible space.

Ran disk tools, no errors, disk management shows partition as healthy, 109 GB. Drive is NOT compressed.

EDIT 2:

Downloaded smartmontools, ran smartctl -H /dev/sda "SMART overall-health self-assessment test result: PASSED" No idea what it means exactly but doesn't sound like half the drive is dead.

What now?

Igor Ivanov
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    Possible duplicate of [printing - How can I visualize the file system usage on Windows? - Super User](https://superuser.com/questions/8248/how-can-i-visualize-the-file-system-usage-on-windows) – DavidPostill Mar 28 '21 at 14:34
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    Does this answer your question? [How can I visualize the file system usage on Windows?](https://superuser.com/questions/8248/how-can-i-visualize-the-file-system-usage-on-windows) – DrMoishe Pippik Mar 28 '21 at 19:43
  • Maybe you could use linux. – bobsfriend12 Mar 28 '21 at 20:24
  • I'll have to try one of those utilities. So far I used Everything! I selected the files that have "modified" date since I freed 10 GB last night, and they amount to only ~ 1.5GB. – Igor Ivanov Mar 28 '21 at 20:28
  • @DavidPostill See edit. Any more ideas? – Igor Ivanov Mar 28 '21 at 23:22
  • @DrMoishePippik See edit. – Igor Ivanov Mar 28 '21 at 23:22
  • @Daniel I found your similar question, were you able to solve the problem? – Igor Ivanov Mar 29 '21 at 00:35
  • @StuartHaydn I found your similar question, were you able to solve the problem? – Igor Ivanov Mar 29 '21 at 00:43
  • If storage is disappearing, it's likely a hardware fault or age. Have you checked your drive health? – music2myear Mar 29 '21 at 03:13
  • @music2myear yes, I mentioned it. checked again "Windows successfully scanned the drive. No errors were found." – Igor Ivanov Mar 29 '21 at 03:41
  • No, Windows is only checking data consistency on the drive. You need to check SMART or if you drive manufacturer has a utility (these are common for SSDs and other modern digital storage) or one of the other utilities that can report dead/retired, remaining over-provisioning, write cycles, etc. Disk Check doesn't cut it. – music2myear Mar 29 '21 at 03:43
  • It's rather straightforward, as I described: once I free some space, it disappears very soon. ~ 20 GB in the past week. No errors ever reported. – Igor Ivanov Mar 29 '21 at 03:44
  • @music2myear Downloaded smartmontools, ran smartctl -H /dev/sda "SMART overall-health self-assessment test result: PASSED" No idea what it means exactly but doesn't sound like half drive is dead. – Igor Ivanov Mar 29 '21 at 04:12
  • Do you have some backup or System Rollback tool running that eats up space? – StarCat Mar 29 '21 at 06:29
  • Can it be file history / backup? On my PC it eats around 50-70 gb of space every week – Magnetic_dud Mar 29 '21 at 14:34

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What are you doing on your computer, in general?

Asking because I had same problem a few years back. I needed to monitor the ODBC drivers and thus I turned on full logging in the setting. Debugging done, I forgot to turn full logging off and then in matters of minutes I ran out of disk space, because it logged EVERYTHING. Like, for example, seven 10GB tables sent over from the SQL server that I connected to using that ODBC. That took a while to track down, I used Total Commander to search for newest created files and ordered them by size. Then I traced back the log file to it's location and then connection clicked.

Since your SpaceSniffer scan shows "Inaccessible space" there may be few issues here, and which I have personal experience with each:

  1. Insufficient permissions - I saw that you said you ran it as Administrator, but there's still a difference between running app while logged as user with Admin privileges and "Run as Administrator" in the context menu. Unfortunately.
  2. Encrypted folders - they by definition will not show as accessible space, simply because that's the purpose of it. Now, if you didn't set up any encryption, then see my comment below about a virus.
  3. Indexing - but this will be immediately apparent by checking the size of Windows.edb file. Not really a possibility unless SpaceSniffer ran with insufficient permissions (see point 1).
  4. Offline files - look in C:\windows\CSC. But again, SpaceSniffer should show that.

The other option that comes to mind is a virus. Someone is using your PC for bitcoin mining... And no, CPU/GPU usage may not show you that, because then you'll know. Those miners use your machine when idling. (at least ones I know).

AcePL
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  • It's a development machine for desktop applications. I don't log anything. The missing space shows up as a black hole i.e. no visible files in it (see message). All accessible files including hidden/system account for half the drive. Virus - possible. Bitcoin mining - don't see CPU/GPU usage. – Igor Ivanov Mar 29 '21 at 13:59
  • @IgorIvanov - see edited answer. hopefully something there will help you. – AcePL Mar 29 '21 at 14:26
  • Thanks for all the suggestions. @AcePL Huh... I signed out of my user account then signed back in and immediately saw 60+ GB of free storage! It didn't occur to me to reboot just for the sake of it because I had a windows update last Tue that resulted in a reboot and I started having problems with low space warnings and errors only afterwards (AFAICR). So far a few hours and all the storage is still there. I'll see what happens overnight, maybe the pest does its mischief out of work hours. Does it look like a bitcoin miner/virus? I'll update my question when I have more observations. – Igor Ivanov Mar 29 '21 at 17:12