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From Peter Crowther <peter.crowt...@melandra.com>
Subject Re: Performance 5.5 vs 6 vs 7
Date Mon, 14 Mar 2011 07:12:12 GMT
On 13 March 2011 21:01, Tony Anecito <adanecito@yahoo.com> wrote:

> As someone mentioned the network can imit you. If your bandwidth
> utilization is
> at 60% or over you are in trouble since collisions start to become a
> serious
> issue.
>
> Collisions may or may not be an issue, depending on the exact mode of
operation of the congested network link.

Collisions are a feature of the original Ethernet.  They're still an issue
on many Ethernets, but there are provisos even here.  If your switch does
store-and-forward, or you simply have a switched network and all the traffic
is between two stations, then collisions are relatively unlikely and the
Ethernet usage can go considerably higher than 60% before collisions and
retries start to become significant.  Sure, if you're on wireless or using
an old 10baseT or Cheapernet hub, 60% is about the knee in the curve.  But
I'd be a little surprised if Dave were using such ancient technology for a
critical piece of infrastructure such as this server :-).

Point-to-point links, such as most broadband connections, do not suffer from
collisions as the routers at each end store and forward traffic across the
link.  That said, by the time you get to 80% usage then each packet is
typically going to have to queue behind several others.  Even if this only
adds a few milliseconds of latency each time, it builds up when you multiply
it by the TCP 3-way handshake, 4-way FIN/ACK sequence, plus any data you're
transferring.

Dave, could you give us any more information about your network?  What is
the piece that's at 80% utilisation when you see the trouble?  Is it a
point-to-point connection, or an Ethernet LAN, or what?  If it's Ethernet,
what hardware are you using for connection?

Tony - I also don't believe 2ms is the best you can get on Ethernet.  If it
was, most big machine rooms would have silted up with network traffic long
ago ;-).  It depends on what network technology you're using.  For example,
gigabit Ethernet latencies are considerably lower than good ol' 10 meg.
What link speeds do you have to your router?  100 Mbit/s?

- Peter

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