Cisco MDS SAN Dual ported HBAs Zoning Best Practices?

[Sara Weylman]

We frequently have servers with dual ported HBAs, and the standard practice has been to split the HBA, half zoned to the A Fab and half to the B Fab.  Recently one of my peers voiced the opinion that doing this contributes to slow drain situations.  Thoughts or opinions?  Is there an established best practice for dealing with dual ported HBAs?  Please advise.  Thank you.

[Walter Dey]

Hi Sara

Best practise (EMC, HP, Netapp,....) is to build a dual FC fabric (and please use different VSAN's for Fabric A resp. B), and then dual home server and storage devices. Zoning is done per fabric (and VSAN) ! Of course this requires proper multihoming software on your host.

[Sara Weylman]

Thank you Walter, let me test my understanding here.  Are you suggesting the creation of a 2nd VSAN in each fabric (we normally use an A and a B fabric with unique VSANs, core edge topology and a C fabric for backups). We have long been battling the slow drain issue, (400 + MDS, mostly 9710s and 9513s) but I'm not convinced this is a contributing factor. 

"A host with multiple HBAs requiring multiple connections must have all ports of the same HBA wired to the same fabric. The WWNs on the HBA are sequentially numbered to help identify ports on the HBA.

Slow drain or faulty HBAs can cause fabric errors or congestion, and if an HBA has a fault condition it can impact both fabrics."

So, are you saying to build an additional VSAN in both A/B fabs and split the HBA but only to the depth of the second (yet to be created) VSAN?  Please advise.

[Walter Dey]

Hi Sara

If one is paranoid about availability, you would have to build 2 separate fabrics with different vendor switches, e.g. Cisco and Brocade, and the each server would also have 2 separate vendor HBA, e.g Emulex and Qlogic. Each vendor has ist slow drain implementation.

I know no customer doing this !

I would ask you: do you really have a slow drain situation (see eg. 

https://www.cisco.com/c/dam/en/us/products/collateral/storage-networking/mds-9700-series-multilayer-directors/whitepaper-c11-737315.pdf 

https://www.youtube.com/watch?v=tijVaIatQgQ) ?

and if not, why bother ?