[c-nsp] Max performance 6148(A--GE-TX boards

[Matt Buford]

> Can anyone comment on this ? Does this mean we can get a max of 6 Gig
> throughput on a 6148A card and max 2 Gbit on a 6148 ? Or do these
> numbers only apply to etherchannels ? I don't seem to find the right
> performance figures for these cards.

Issue 1:

Each group of 8 ports only supports a gigabit.  If you get 2 ports in the 
same range of 8 both trying to download a gigabit, each one is only going to 
receive 500 mbits.  If you have a mix of high bandwidth servers and low 
bandwidth servers, you should probably spread the high bandwidth servers out 
so there is only one big bandwidth user per group of 8 ports.

Issue 2:

When using etherchannel, a copy of EVERY PACKET for the entire etherchannel 
bundle gets sent to the ASIC.  Since the ASIC only has a 1gbit capacity, 
this means that the entire etherchannel bundle maxes out at 1gb.  But wait! 
It isn't just the etherchannel bundle that maxes out at 1gb.  It is the 
etherchannel bundle plus all other ports on the same ASIC.

The result:

So, lets imagine you make an etherchannel with port 3/1 and 4/1.  Both cards 
are 6148-GE-TX.  Your etherchannel downloads at 1gbit.  Now, someone else 
(not in the Etherchannel) on port 3/2 starts downloading.  The downloader 
AND the etherchannel now have to share the 1gbit restriction, since the ASIC 
handling 3/1-8 has to receive a copy of every etherchannel packet plus every 
packet for port 3/2 - all through a 1gbit pipe.

The moral of the story is don't etherchannel on WS-6148-GE-TX cards (unless 
doing so only for redundancy and not for bandwidth).