I've been seeing some disparity in disk space between pairs of mirrored discs. After using FolderSize, I was able to see hundreds of GB of files in one of the mirrored disks, but not in it's twin. I was able to delete them using this tool, however I couldn't see the files from Windows. I had unchecked hide system files, etc. and used the disk cleanup tool to empty the recycle bin, but it did not affect these files, which appeared to be in folders that were recovered after a disk crash and which I did not delete.
Can anyone explain what happened?