I'm trying to allow my website to write to a microSD card I have inserted into my Guruplug.  I can write to the card as root, but www-data cannot write to anything on the usb even though I have run chmod 777 on the folder I want it to write to.  If I try to change the ownership of the folder to www-data I get "operation not permitted".  The website can write to the onboard flash in folders other than /var/www, but I'm not sure why I can't write to my microSD card.  Any ideas?