Fibre Channel (SAN)

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Contributor
Posts: 45
Registered: ‎06-04-2012
Accepted Solution

Core-Edge Topology Concerns

- We have 4 * 6505 Brocade switch into two fabrics(2 switch each). Right now, if we take one fabric, in one switch (SW1) only server ports are connected and on other switch (SW2) both storage and server ports are connected.
- Now client puts a proposal to change it to core-edge topology where all servers ports from SW2 will be removed and re-connected to SW1. And I was supporting with that proposal since it is standard and some benefits are there.
 
- But, one of my colleague who is another SME says he is not happy with that proposal, since bringing all the servers ports on one switch will increase load on ISL. He further said that we will distribute the storage and servers on both the switch which will be load balancing.
 
 
Now, I would like to show him the real figures or stats and some evidences to prove that core-edge topology is correct. What data should I collect and what extra points can I put to support this model? We have BNA for these switches.
External Moderator
Posts: 5,266
Registered: ‎02-23-2004

Re: Core-Edge Topology Concerns

@DattaSai

 

both proposal, you and from a client are not the best practices, for a simple reason, you have just TWO Switch each fabric.

 

the best solution is follow:

 

Fabric_A:

 

ISL both Switch_1 and Switch_2

 

distribute each one Array Controller 1/ 2 Port  A /A ( usually you have 4 Array Port each TWO per Controller ) to Switch_1 and Switch_2

 

distribute each HBA Port to Switch_1 and Switch_2

 

the same design for Fabric_B:

 

TechHelp24
Contributor
Posts: 45
Registered: ‎06-04-2012

Re: Core-Edge Topology Concerns

Thanks a lot Antonio. But in that case, if host and array ports are distributed, will it not be difficult to identify SDD (slow drain devices). In Core-Edge (MAPS) design, it will be easy to identify SDD, isnt it??

 

 

Regular Contributor
Posts: 166
Registered: ‎02-05-2014

Re: Core-Edge Topology Concerns

A core-edge design is only good for one purpose: To make it look good on Visio diagrams.

 

A SAN design with performance in mind should make sure that locality of reference is applied which basically means to put initiators and targets with these highperformance requirements as close as possible to each other preferably on the same ASIC and in the same port-group.

 

ISL's should only be used in case physical restrictions apply (like switch placement in a datacenter) or if cross functional storage architectures are in play who's ports are connected somewhere else. (tape/vtl systems is an example.)

 

Slow-Drain then also has muchless influence on traffic as back-pressure is concentrated in one ASIC and therefore will not flow onto ISL's and other parts of the fabric.

Kind regards,
Erwin van Londen
Brocade Distinguished Architect
http://www.erwinvanlonden.net The Fibre Channel blog



Q&A -> https://hackhands.com/elo/


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Contributor
Posts: 45
Registered: ‎06-04-2012

Re: Core-Edge Topology Concerns

Thanks Ervin for the reply.

 

Its not possible to keep all initiators and targets in the same portgroup/ASIC as there are large number of Initiators while the targets are few in number.

 

Considering we have 2 * 6520 switches, On 1 switch all initiators(most of them are access gateway NPIV) and on the other switch it is a mix of both initiator and target. The 1st switch is fully populated with very few ports left, whereas the 2nd switch has 30+ ports free. In this scenario (4 * ISL's between two switches) what is the best way to distribute the switch ports or leave it as it is.

 

Also how to calculate the number of ISL's required between the 2 switches? Any formula to calculate?

 

Thanks!!!

Regular Contributor
Posts: 166
Registered: ‎02-05-2014

Re: Core-Edge Topology Concerns

There is no formula to determine the required number of ISL's.It all depends on workload. The more you can concentrate workload withina switch the less ISL's you need and the better performance you will have plus you leave more port for end-device connectivity.

 

Look at the provisioning ratio on initiators and targets and try to consolidate this ratio as much as possible onto a switch. Balance it evenly over the amount of switches you have and you're pretty safe.

 

 

Kind regards,
Erwin van Londen
Brocade Distinguished Architect
http://www.erwinvanlonden.net The Fibre Channel blog



Q&A -> https://hackhands.com/elo/


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