recommended cabling setup and 10G ethernet?

Hi All

couple of questions

What is the difference between a stock data domain system and the 10G models?

Is it just the additional 2 x 10G ports together with the 4 x 1G ethernet ports?

Why would one choose to use the additional I/O cards on the DD system over the onboard ports? (HA?)

for example assuming the above is correct for the 10G model - could someone give an example of where a need would arise in which an additional 10G (dual/quad) card will be needed?

Just wondering how others have cabled their systems..

thanks