WinDirStat shows 244GB unknown space on external drive

Instead of windirstat you should use TreeSizeFree.

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

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.

In my case it's the Windows search file, Windows.edb, in: \ProgramData\Microsoft\Search\Data\Applications\Windows.

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.