9134 b2b credits

Unanswered Question
Jan 17th, 2008


Having come from a director class environment, I have to wonder about b2b credits on something smaller like the 9134. It has 64 available per port group which consists of 4 ports. If I intended to purchase something like the 9134 for purely ISL work with FC and FICON, how can I get around this b2b credit issue? I have had nothing but problems with HDS True Copy in our normal (Brocade) fabrics and I have decided to split the replication onto its own "SAN" with ONS 15540 providing the DWDM links. Brocade provide either R_RDY or VC over ISL's and I am not convinced that VC can handle head of line blocking. R_RDY definitely cant as it is not capable of that function. So if I was to run port channels of say 2 x 4 Gpbs over up to 32 kms, my 64 b2b credits is not going to leave anything for the other two ports per port group.

10 Gpbs ISL's seem to be the way to do this.

Any comments are most welcome.


I have this problem too.
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dmcloon Thu, 01/17/2008 - 23:20

I dont this 9124/9134 is good choice for long distance ISLs. 20-30km is OK.

stephen2615 Thu, 01/17/2008 - 23:38

Hi Dallas,

I gather you meant to say I don't think the ... is a good choice.

Our DWDM links are in a circle with 8 km one way and about 35 the other way. What is the method for working out B2B credits? I thought it was 1 credit be km per Gbps. So what would a 4 Gbps link over 35 km need??? Is that 140 credits? Even half that many is 70 which is more than 64 per port group.


dmcloon Wed, 01/23/2008 - 17:44

Yes 9124/9134 is not good choice for DWDM @ 4Gbps.

At 4Gbps you need 2 B2B credits per km. So 35km is going to require 70 B2B, already over the limit. If you run it at 2Gbps you will be OK, but only one ISL per port group.

stephen2615 Tue, 01/29/2008 - 23:00

This leads me to the 9134 10 Gpbs ISL. If it has 64 buffer credits, what good is it? That equates to about 5 buffer credits per kilometre. Thats a limit of about 12 kilometres. Considering that the practical native fibre channel standard is about 32 km in most cases, I would expect enough buffer credits to handle that distance.

The 9222i is just toooooo expensive as I don't want the IP connectivity. Pity..



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