[CentOS] USB drive is "read-only file system" and cannot umount - how to fix

I 'just' noticed that at some point, my USB backup drive on my server
>is 
>mounted as read-only and all of my background sync cron jobs have been 
>failing.
>
>So I need to fix this without rebooting the server.

>How can I get this drive r/w?

Have you tried "mount -o remount,rw <mountpoint>"?

The unanswered question here is why did it go read only, and does this condition still exist?

Barry