[cobalt-users] Can you explain this please?

["Casselman, Chad" <chad.casselman@xxxxxxxxxxxxxxxxx>]

I got this error last night, but when I got to system status everything is
all green.

The disk is nearly full; an amber warning light means that more  than 80% of
your free disk space is in use; a red warning light signals that more than
90% of the disk is being used.  You either need to move some files to
another storage device and delete them from the Cobalt server or else delete
them altogether.

Can you please explain why I might be getting this and how I can fix it.
Thanks,
chad