I'm toying with a scenario where I want to backup several terabytes
daily in a NetWorker enviornment.

Some facts,
Clients: several hundred of many different OSes
Data volume: about 20 TB needs to backed up during a lot less than 10
hours, I'll probably aim for 5 hours. That's 4 TB/hour or approx 1120

I plan to use one or more virtual tape libraries as a storage device,
each one can give me 300 MB/s sustained write speed.

I plan to use several dedicated storage nodes. The storage nodes are
backing up the clients over the LAN. I will not use a dedicated LAN
segment, I don't see any point. With clever placements of storage
nodes I can pull the clients over the backplane.

The storage nodes will be centrally managed from a NetWorker master
server, but the master server will be busy handling index and I don't
want to use the master to move data as well.

Question is, how many storage nodes do I need to have a combined
throughput of 1120 MB/s. I can probably trunk a few GbitE connections,
but do I trunk 2 and hope for ~150 MB/s or can I go with even 4 GbitE
and hope for ~300MB/s. In any case I want to use x86 hardware and
scale out instead of buying some huge box and scale up. OS on these
boxes is a pretty open subject, but something tells med Linux would a
be good choice. These boxes are truly dedicated for the task, they
will not be running any other applications.
Could I hope for a 4x Gig trunk on a 2 CPU machine, some AMD dual core
variety are dirt cheap these days. On the backend I'll use 4Gbit Fibre
Channel to stream the data to the VTL.