Server is running low on available disk space

My system (ClearOS V7.3.0) has started popping up with the message

Ooooops: Server is running low on available disk space - preventing further modifications via API until disk space issues are resolved.

.

My system summary shows the /dev/mapper/clearos-root as being 100% used. This is a 1Tb solid state drive. The biggest directory is my VAR at 165Gb, but the next biggest is the USR at only 2.3Gb. In total, i shouldn't be using more than 200Gb.



I ran the command below, but this didn't highlight anything other than my flexshare folders.


I just can't seem to see where 916Gb is being used. Any ideas?