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Re: Bandwidth issue

tClancey
Tutor

Bandwidth issue

Hello again.

 

I've jut been doing some testing with the 128 raspberry cluster and the switch setup.

Quick introduction:  128 raspberry pis connected through 4 GS748Tv4 switches which are stacked by both fiber lines and 4x gig ports in a chain.

 

I'm testing with iperf, bidirectional, from one master pi to others.

 

If I test from a pi on the same switch the throughput is around 4.2 Gbits/s

If I test from a pi on switch 2, 3 or 4 the throughput is around 136 Mbits/s

This is a huge loss.

 

My belief when choosing these switches was the fibre links alone would be able to channel data better than this.  Am I missing something?  Have I missunderstood what the lags should be capable of?  Is there a problem with my fibre modules/cables?

 

If I pull out the 4 gig port chain the results are no different.  So no data is being sent on those and are probably pointless?

 

Any ideas?

Model: GS748Tv4|Netgear 48 ports Smart Switch
Message 1 of 7
schumaku
Guru

Re: Bandwidth issue

AFAIK the Smart Managed Pro devices are not stackable. Instead, both standalone managed switches can be connected regardless using a single configured LAG. Blunt theory, it's not advised to mix different speed/latency/media into a single LAG (e.g. fiber plus copper). So how are the switches connected, how is the LAG configured?

Message 2 of 7
tClancey
Tutor

Re: Bandwidth issue

Thanks for your reply.

 

I've tried variations, at the moment the Lag on switch one is port 2, 4, 6, 8, 48, 50 down to the next switch, switch 2 has two lags, 1, 3, 5, 7, 47, 49 up, and 2, 4, 6, 8, 48, 50 down, etc.

 

So you shouldn't mix fibre and copper, I'm guessing with this setup the copper is just being ignored as there's difference if connected or not.

 

And no, these aren't stackable switches, but I was reliably informed (I thought) that they could be chained with no (or very little) loss of speed.

 

Would I be better connecting switch 2, 3 and 4 directly to 1 and lose the chain?  This would mean only using one fibre link per switch.

Message 3 of 7
tClancey
Tutor

Re: Bandwidth issue

Actually, if you read the blurb the switches are stackable, with the fibre ports.  More testing needed....

Message 4 of 7
schumaku
Guru

Re: Bandwidth issue

Yes of course, we talked on the LAG to connect multiple switches. Nothing uncommon. Chaining, hub and spoke, or ring, or any kind of combinations are possible.

 

What I was behind - are the LAG configured as LACP, do all loag show fully up with all links workable?

Message 5 of 7
tClancey
Tutor

Re: Bandwidth issue

No, I think I'm wrong, the T version doesn't.  Well, F. it!  There's 4 748 switches going to hit ebay next week!

Message 6 of 7
schumaku
Guru

Re: Bandwidth issue

Doesn't make sense - something is borked with the LAG config.

Message 7 of 7
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