[TriLUG] OT - gigabit switches

Christopher L Merrill chris at webperformance.com
Thu Sep 21 10:19:59 EDT 2006


Wow!  What a great bunch of responses, especially those from Greg,
Ryan and Aaron.  Most of it was over my head...but I'm hoping to absorb
just enough to make an intelligent decision for our test lab.

I've tried to identify which specs of a switch are actually important
for our use-case.  To recap, we're are moving towards having (at most)
20 computers in our test lab with GigE NICs (some with multiples).
When we care about the performance, the scenario will be that most
of those computers will be hammering one or more web servers, also on
the same switch, with as much traffic as it/they can handle.  In some
cases, each "load engine" will be aliasing multiple IP addresses on
each NIC.  All of the machines will be on the same subnet.  When we
run tests, we would like the network to be invisible...meaning that
it is never the bottleneck.

So I've seen a few specs mentioned in switch literature and mentioned
in the discussions -- I am trying to assess how those relate to our
situation.
1. MTU - larger is better to improve bandwidth efficiency
2. # of MAC addresses - since we have a small number of computers
on a small network, I would guess this is unimportant to us.
3. Switching Capacity - pretty important to us, I would think, but
also seems to be the same for all models within a given line from a
given manufacturer - is the published number meaningful?
4. Forwarding Rate - I have no idea what this is...important?


One other point that I wanted to verify is that one of the jobs of
the switch is to keep traffic away from parts of the network that
are not involved with the sender or receiver.  For example - the
switch in our test lab is hooked to the switch for the rest of the
office, to which the rest of our desktops are connected.  So when
we are running tests in the lab, none of that traffic bleeds into
the rest of the network affecting performance there.  My
understanding (and anecdotal evidence) is that this is true...is it?

TIA,
C


I wrote:
> We would like to upgrade our testlab to a gigabit switch.
<snip>



-- 
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Chris Merrill                           |  Web Performance, Inc.
chris at webperformance.com                |  http://webperformance.com
919-433-1762                            |  919-845-7601

Website Load Testing and Stress Testing Software & Services
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