two MDS switch with or without ISL

[ciscomdsmagic]

With only two MDS switches, what differences it would make in cases with ISL connection in between, and without such connection?

If I make any zoning updates on one switch, would that automatically be updated on the other if there is no ISL?

Thanks for help!

[dynamoxxx]

how do you think switches communicate to each other ?   By connecting two switches together you are creating one fabric, if you expect any kind of high availability you need to keep fiber channel fabrics separate.

[ciscomdsmagic]

I am sorry, but I don't quite understand you. I am new to MDS SAN.

One side, it seems that I do need to use ISL to communicate each other, and it will be creating one fabric.

However, on the other side, you said that I need to separate them to have high availability. why I could not achieve high availability by connecting two together?

[dynamoxxx]

take a look at "popular documents" on the right hand side

https://supportforums.cisco.com/community/5636/storage-networking

[ciscomdsmagic]

Could not find one which fit in my answer.

Can anybody please help me to give me straight answers. Thanks,

[Walter Dey]

see eg. Figure 10. SAN Booting for Cisco Unified Computing System Servers

in http://www.cisco.com/c/en/us/products/collateral/storage-networking/mds-9500-series-multilayer-directors/white_paper_c11_586100.html

It's referring to UCS, but a server with dual homed hba's is a general concept. 

[ciscomdsmagic]

Walter Dey,

based on the provided link, it sounds there is no need to create ISL between two SAN switches, which means to me that there are two separated fabrics, and zoning configurations are separated as well, changes made in one switch/fabric will not have impacts on the other.

In this case, a multipathing software on hosts will control/switch the path to the other fabric if a  link in one fabric went down.

Please let me know if I am wrong.

[Walter Dey · Accepted solution]

You are 100% correct !

please use 2 different VSAN's on the 2 MDS, different from 1 ! this is state of the art. As you said, zoning is done per fabric (and vsan), therefore you have total isolation.

Multipathing on the server will do HA (loadblancing and failover, in case a fabric would fail).

Walter.

[ciscomdsmagic]

I am sorry to pick up the thread again. I have learnt a lot, but for my original question.

without ISL between these two switches(two fabrics), how could they communicate and know each other's zoning configurations? or is there any need at all to communicate?

I have one VSAN (not vsan 1) one activated zoneset in each switch.

[Walter Dey]

If you have 2 isolated MDS (no ISL); you have zones/Zoneset and a active zoneset per MDS. They are isolated from each other, and don't need any information exchange. This is the idea behind 2 separate fabric.