Windows reports incorrect free space on a disk

I had an interesting one today. Received a call for a disk that is running out of disk space and I thought, easy, quickly log on and clear some space.

It turns out that the total data on the disk was 5GB in size, with the disk being 40GB in capacity, but the available free space reported was 4GB. This baffled me a bit but after some assistance from an internet search and colleague we quickly found that the problem was related to shadow copies taking up space.

In our scenario, shadow copies were disabled but running vssadmin list shadowstorage in the cmd line told us a different story. The output showed that shadow copies was indeed taking up most of the disk space.

To resolve this we enable and disabled shadow copies for the disk. Set the limit for shadow copies to a small amount of disk space and then enabled shadow copies again.

Voila! We got back our used disk space.

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