Windows 10 - C drive full but no files

Question

Last week I've noticed that my C drive was out of disk space. So for the past few days I've been looking into what folders occupy my disk space, and started cleaning up a bit. I've ended up freeing 75 GB.

Ever since, I've seen that my efforts to free up disk space were useless. Today already, I'm right back at only 12 GB free disk space again. Once again I've started looking into what folders are taking up space.

Read this picture as follows:

• Invisible files/folders are shown in Windows Explorer
• My SSD has a capacity of 475 GB
• All files/folders on my disk are taking 166 GB (only 1/3 of my capacity)
• My disk is full

Why does this keep happening? Where do these 309 Gigabytes go to?

I'm a .NET developer, so I do have SQL-server installed, but even so, the file size of the SQL-server cache folders should show up in the measurements.

EDIT

I did a scan using the tool that @Señor CMasMas suggested (run as administrator)

And it's indeed the folder C:\Program Files\Microsoft SQL Server\MSSQL15.MSSQLSERVER\MSSQL\Log\Polybase\dump that's taking up all disk space (literally 256 GB), even though you can't see it under the Program Files folder size.

EDIT 14/06/2021

I had installed the latest version of SQL Server. Now we're 3 weeks in, and once again my C drive is getting seeded with the same file:

Answer 1

There are plenty of tools available to help diagnose lost disk space.

One such tool which I've used for many years (more than I care to mention) is TreeSize. They have a free version, which you can download from here.

Scan your C:\ drive, and order the results in descending order by size. If pagefile.sys or hiberfil.sys turn out to be the offending items, look at moving your pagefile off your SSD, or capping its size, and/or disable hibernation.

Alternative tools include but aren't limited to SpaceSniffer, windirstat, ...