I have an external (non-system) drive with whole disk Truecrypt encryption.
When I mount the NTFS volume there is no option to compress contents in the drive->properties. And truecrypt mounted volumes don't show up in computer management->local storage.
Individual files and folders have the 'compress contents' box but it is disabled.
Is there any reason why you can't compress inside a truecrypt volume?
(Windows7, truecrypt 7.1, running as Admin)