A drobo isn't a bad idea.
If you are gonna be doing automated offiste backup you are gonna have to get a better net connection with faster upload. The first time it would probably be easier to physicaly transport the data to the offsite data center as the volume of data would be so large. Then all the other backups would be smaller incremental ones.
If you end up a with a file server running *nix rsnapshot is a good tool to use.
Need a sig