Extreme Slowdown using Gb Network

Seumas Macmhicean seumas at realise.com
Tue Mar 25 10:16:01 CST 2003


I'll reply to a couple of responses at once - thanks all for promptness!

>You said that "all other boxes on the network experience a crippling
>slowdown" when copying large files.  Do you mean that Box C is slow
>delivering data to the public network when Box A is copying files to Box
>B on the private Gb network?  Or is Box C slow in talking to Box D on
>the private network when the transfers are happening?

To clarify - when copying largish files between boxes A and B, all other
boxes become
very unresponsive in general usage - reports on CPU, disk, network and so on
all appear normal.
Nothing appears in dmesg nor messages, but the other boxes chug - even doing
a simple 'ls'.

>What do the network traffic lights look like on both switches?

It's in the Co Location facility... will have to check another day

>Is there anything strange in the output of sar -n eth[01]? on both the
>transfering and non-transfering systems?

We're going to investigate this.

>You could be having problems with the nics advertised auto-negotiating and
having problems with renegotiating
>during a heavy network load.

We're looking at ethtool but it seems to break the interface - we'll keep at
it and see if we can switch off the autonegotiation since we don't need it
(all devices on the network are the same - tg3)

>This may sound like an obvious step, but have you verified that you are
using cat5E and not cat5 on these?

Interesting point - the cables were bought new for this build and are about
2 months old - will have to check them explicitly (again - Co-Location
facility) but aren't they all Cat5e compatible nowadays? Still, something to
check.

>Which model switch?

NetGear GS516T - bog standard config-free Gb switch

>Possibly, but any modern network switch acts as a multi-port bridge, so
>your other boxes should not even see traffic. 

Of course... but the effect is there - we'll do some more thorough checks to
make sure though... Hmmm. Faulty switch?

Something very odd is afoot here...

Seumas



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