Move from Edge-Core to Edge-Core-Edge without interrupting fabric traffic

[michael.clapp]

I need to add another switch to our fabric for growth.

I am currently in a Edge-Core model.

I have a 9396 for a host edge.

I have a 9710 acting as a core with ISLs to my 9396 and storage directly connected.

I need to move to an Edge-Core-Edge model, preferably without interrupting traffic on either fabric.

I am currently considering the following process

I would be performing this process on both of our fabrics, one at a time.

1. Install new 9710 to use as a core

2. Set up ISL to 9396 host edge

3. Set up ISL to 9710 (Old core, new array edge)

4. shut ISL from 9396 host edge to 9710 (Old core, new array edge)

5. Traffic now flows from 9396 to 9710 new core to 9710 array edge (old core)

Is there a way to get traffic to prefer the new, more hops, edge-core-edge path so the ISL between the two edge switches is not used?

If there isn't a way to set a preferred path gracefully, will I lose frames if I just shut the ISL between the two edge switches?  

I know I could stop traffic on the fabric and remove the ISL between the edge switches, but due to business politics, I'm attempting to do this without traffic interruption in either A or B fabric.

Thanks in advance for the advice.

[Walter Dey · Accepted solution]

Hi Michel

Sorry, I don't understand the details of your procedure; can you please create a diagram initial - final state.

Of course, you can change the cost of a ISL link and therefore determine the preferred path. FSPF is the FC routing protocol achieving this. see e.g.

https://www.cisco.com/en/US/docs/storage/san_switches/mds9000/sw/rel_3_x/configuration/guides/cli_3_3_1/fspf.pdf

Walter.

[michael.clapp]

Changing the cost of the link is exactly the information I needed to find.

I have a 9396 with all my hosts connected to it

I have a 9710 with all my arrays connected to it

I have an ISL connecting the 9396 and the 9710

To expand my fabric, I need to insert another 9710 to act as a core switch with my two originals now functioning as edge switches.

Set up an ISL from the 9396 Edge to the 9710 core

Set up an ISL from the 9710 edge to the 9710 core

Change the cost of the ISL from 9396 edge to the 9710 edge to be much higher so traffic will stop using that route and instead flow through my new core switch

Remove the ISL from the 9396 edge to the 9710 edge

See attached JPEG for details