How to verify transmission quality & cables on gigabit network?

[Joel Jaeggli]

On Thu, 27 Apr 2006, Rob wrote:

>
> Hello,
>
> I have a cluster, master + 8 nodes, connected via
> a Netgear Gigabit Ethernet Switch (model JGS516).
>
> The cables are of CAT5 type.
> Elsewhere I read that for a gigabit network, one
> should use CAT6 type cables, to avoid bad
> transmissions. Is that so?

Not really. The symbol rate for gigabit ethernet is actually the same as 
100Mb/s ethernet, (125mhz) and should run for similar distances over the 
same cable. using "better cable" buys you squat if your bit-error rate is 
currently zero...

> I already have done basic speed checks, that indicate
> a throughput of about 0.5 Gbps. Hence the network
> appears to operate on half of its spec. speed.
>
> Question 1:
> Should I worry about this reduced speed?

Are your cards in 32 bit 33mhz pci slots?

In general that's about what you can expect without careful selection of 
the hardware involved.

> Question 2:
> How to check the transmission quality?

Do you see errors in any significant rate on any of your interfaces? 
Duplex mismatches are rare with gigabit ethernet,

> Should I inspect the output of "/sbin/ifconfig eth0"
> for errors/dropped/overruns/collisions etc. in the
> RX/TX lines?

If your error rates increment rapidly while sending data then yeah you may 
have an issue there.
>
> Lan card info:
> master: Tigon3 10/100/1000BaseT Ethernet
>   tg3: eth0: Link is up at 1000 Mbps, full duplex.
>   tg3: eth0: Flow control is on for TX and on for RX.
> nodes: Realtek RTL8169
>   eth0: Auto-negotiation Enabled.
>   eth0: 1000Mbps Full-duplex operation.
>
>
> Thanks for advice and help!
> Rob.
>
>
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Joel Jaeggli  	       Unix Consulting 	       joelja at darkwing.uoregon.edu
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