Expanding Fabric

Unanswered Question
Oct 14th, 2008
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I'm fairly new to SAN switch configuration so hopefully I don't come off as an idiot.

Our current environment consists of two 9513s that are totally independent of each other. Each has multiple connections to a CX3-80. We are adding a CX4 in a different building (fiber between buildings) and have purchased two 9134s to put in the new building with the new CX4. I guess my question is what is the best configuration of topology to make that:

-allows storage arrays connected to the 9513s to be able to communicate with storage arrays connected to the 9134s.

-provides the easiest management

Lastly i'm a little confused about exactly what happens when you create an ISL link between two switches. for example if i connected one of the new 9134s to an existing 9513 would it immediately create one fabric?


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inch Tue, 10/14/2008 - 14:27
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First of all you will need to know the distance and type of fibre optic cables between the two rooms to ensure you have the correct optics for the cable/distance.

Second, are you going to be using the 10gb connections for some 4gb connections?

If you are using some 4gb connections i suggest you bundle at least two (pref 3) ports into what is called a port-channel. A port channel aggregates multiple ports into one for performance and redundancy.

Create a new VSAN for trunking traffic to the new switch (this way you can slowly migrate vsan's across the new switch)

Ensure your 9513 has its switch priority set so it will always be the principal switch.

To you last question, depending on VSAN's configured and switch priority it would create "one fabric".

If you want a diagram to make this any clearer let me know.


dseagren1 Wed, 10/15/2008 - 05:42
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Thanks for the reply. The connections would be 4gb. I think since the 9134s don't support IVR the 9134s would have to have the same VSAN that the 9513s have in order for hosts to be able to communicate across buildings. Can you point me to any documentation on the configuration needed for connecting MDS switches? I've been through the Cisco site and can't find much other than some generic ISL and trunking info.


inch Wed, 10/15/2008 - 13:37
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I was not suggesting to use IVR, mearly creating a new vsan which is used as the default VSAN for trunking purposes (thing of the native vlan in dot1q).

Attached is a really quick picture I put together.

As far as documentation goes, the online command reference and manuals are the best bet.

Before going ahead, feel free to post the commands you intend to run :)



dseagren1 Wed, 10/15/2008 - 13:52
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Thank you for the reply. I will read through the command reference more. My biggest concern will be to no interrupt service or overwrite some settings on the 9513 during this addition.

inch Thu, 10/16/2008 - 01:43
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If you ensure your 9513's have the correct switch priority configured and perform a single change at a time you really can't go wrong :)



stephen2615 Tue, 10/21/2008 - 22:52
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I see that the distance question was never answered. Its very important especially for cheaper switches. Any distance over 10 km may need a bigger switch. The smaller switches only have 64 buffer credits per port group and at 4 Gpbs speeds, you might need more buffer credits than your switch has.

Any alternate paths in your fibre also need to be calculated. Eg, ours is a 35 km alternate path. While it is not used as part of the day to day operations, if we lose the short path or it flicks over for any reason, I need enough buffer credits for 35 km. 1 x 4 Gpbs ISL needs 70 buffer credits just to handle normal operations.

This is something that Cisco needs to keep in mind when they EOL the MDS 9216A. I don't want to purchase a 9222i if I don't need IP connectivity. I can use native fibre connections with the 9216A over our DWDM network very well indeed. Same would go with a much less expensive CWDM link.

Just something to keep in mind...

dseagren1 Wed, 10/22/2008 - 05:14
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Thanks. The distance is only a few hundred meters.


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