Want to add a 6 TB G-Raid (Mac os extended) ext drive to a 2Tb time capsule, using a powered usb with the TC usb port. Using the airport utility 5.6 on iMAC (10.7.3). Went to manual setup,then disk. Have options of the TC or 6TB. Won't allow update to the 6TB
I am not 100% what isn't allowed.. but I am assuming you want to spread the backup across the two disks.. internal TC and 6TB external.. this is not possible.. It has to be one or the other. TC has no way to build a raid JBOD or anything else. Nor would you want to as that is the most likely to fail and kill your data.
Let me add, backing up 6TB over USB on TC.. will be the most excruciating experience of your life.. cf child birth or passing kidney stones.. large ones.. being the male equivalent.