Yeah that's quite big .. I assume you are operating on bare metal not vmware.
Have you considered splitting the .DATs across multiple NFS servers and performing a coordinated snapshot across all of them, and then backing them up with multiple agents? I'm not sure of the viability of this just a thought I've been having as we approach larger sizes too.
You may also simply be able to create multiple clones of the SNAP and back segments of the image up in each with multiple media agents. You are, however, inevitably backing up the full .DATs each time as you've no method to determine the changed blocks here.

Is this not a bug? A change to a default port number without prior warning should be reported as a bug, no?

Worth adding here obviously that although all of the above commentary is absolutely still true of IRIS, the above scripts don't work with IRIS because the command names have changed. We are working on local changes to our own scripts to support freeze/thaw of both platforms with the same script but that's not completed yet.

Cheers!