Why Cris-Cross between MDS & FI is not supported ?

[Gonuguntla Gopi]

Dear Friends,

Although i read the documents why cris-cross is not supported, But still not convinced.

I have attached the sample architecture with 2  vsan's 20,21 in each FI & MDS . 2 Port channels for one for each vsan in each FI. 2 Port channels in each MDS with particular vsan with trunk off mode.

B200M4 blade with 4vHBA's.  I think that this architecture should work. Because i am mapping the port channel with right vsan & right MDS . 

Experts please give your views. Why this will not work.

[Walter Dey · Accepted solution]

Hi Gopi

This will work, but it contradicts the long history of FC storage design:

You should build a separate dual fabric; meaning vhba1 (vsan10) left fabric, vhba2 (vsan20) right fabric; FI-left (vsan10), FI-right (vsan20), MDS left (vsan10), MDS right (vsan20).

And your server and storage are dual homed to left (vsan10) and right (vsan10) fabric.

Walter.

[Gonuguntla Gopi]

Dear Walter,

Thanks alot for the info.I agree with your answer. Although it contradicts.

But, assume if the FI-A which is on left & SAN Switch-B which is on right is faulty or failed, then the entire infra will be down.

What is the best possible design  where i can eliminate this failure ?

Below is my thought process for larger/critical infra

Do you want us to propose 2 Pairs of MDS Switches ( Each running on different VSAN ) + Two storage controllers with 4 FC ports on each controller. So that i can connect 2 ports per controller to per MDS.  Followed by 4vHBA's on each blade. 

I hope this is the only way out if there is a contradiction right ?

Regards,

Gopi G

[Walter Dey]

Sorry, maybe I was not clear

But, assume if the FI-A which is on left & SAN Switch-B which is on right is faulty or failed, then the entire infra will be down.

The FI's are not dual homed to the 2 MDS, but FI-left is only connected to MDS-left, same for right ones; therefore if a FI and/or MDS fails, there is only one fabric down, and multipathing software on any host will handle this.

Do you want us to propose 2 Pairs of MDS Switches ( Each running on different VSAN ) + Two storage controllers with 4 FC ports on each controller. So that i can connect 2 ports per controller to per MDS.  Followed by 4vHBA's on each blade. 

Yes ! you could do a pc between FI and MDS; I don't see any reason to have 4 vhba's; 2 are enough; a vhba can only be assigned one vsan; therefore one connecting to left (vsan10) the other to right (vsan20) fabric;

No ISL links between the 2 MDS !

Installation of multipathing is essential !

[Gonuguntla Gopi]

Walter,

Let me re-phrase.Even if i do as said above. Still the infra will be down, post configuring multipath also.

Kindly find the architecture enclosed. Because of this i was telling that infrastructure will be down if we cannot have 4 MDS switches.

Please find both the architectures with description.

[Walter Dey · Accepted solution]

Hi Gopi

OK, understood ! However, the probability that a FI AND a MDS fail at the same time is very small indeed. They have a different Firmware, mostly different hardware components,.....

You proposal is very complex, has more components to manage (which could also fail), and last but not least, the multipathing configuration becomes challenging as well.

Therefore I still would recommend what I described in a earlier not, see also

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