Ask the Expert: SAN (Connectrix), FC Connectivity Recommendations and Best Practices

Welcome to our newest ATE session on ECN. We'd like to open this discussion for replies. Let's make of this an opportunity to respectfully engage our experts with your questions, comments or ideas. Have a great experience!

Felipe,

Do you see a lot of customers adopting SmartZoning ?

Thanks

Hi dynamox ,

First off thanks for your query. The fact is that, although this feature is pretty useful, not many customers use it: mainly customers with a big SAN to manage take the step to introduce Smart Zoning.

For those of you who are not familiar with the concept of Smart Zoning, the following link provides a nice description of this feature introduced by Cisco in NX-OS 5.2(6).

By using Smart Zoning, the size and manageability of zonesets can be drastically decreased, specially when using clusters that share targets (storage ports) among several Initiators (server HBAs). With Smart Zoning, you can configure a single zone containing all the Initiators and targets in the same cluster (eg ESX farm) and the switch itself prevents the Initiators from seen each other even though they're in the same zone.

Rgds,

Felipe

I don't have a big SAN (one 9513 core and a few 9148 edges) and i have been using SmartZoning for 2 years now. It is the best thing that has happened to zoning in a long time .  It was very easy to enable SZ on a running VSAN too,  "traditional zones co-exist with SmartZones in the same zoneset just fine.

Hi Felipe,

a customer has upgraded to FOS 7.x, and needs to know if, with the new version, they still need to take care to manually config the parameter fillword to value = 3.

Thanks mate!

Manu

Good evening Manu,

That's a good one, because there is a little bit of confusion with it. The answer to that question is:

• 8G Switchs with Condor2/Goldeneye2 ASICs require to have the fillword parameter set manually, no matter what FOS release they're running.
• 16G switchs (gen5) with Condor3 ASICs automatically set the correct fillword. Only FOS 7 is supported on these switchs.

The fillword is a FC primitive [in plain language, pre-defined frames] used to keep the link synchronized. It became renowned when Brocade introduced the family of switchs that supported 8G. When working at 8G, the FC standard states that the fillword to use is ARB (whilst previously it was IDLE). With 8G Brocade products, this fillword has to be manually configured and when Brocade released the new set of 16G switchs, the fillword is automatically configured, so in a few years time, we will forget about this parameter and live happily oblivious again.

When it comes to EMC products, the recommendation is to configure the fillword with a value of 3 when working at 8G.

Rgds,

Felipe

Hello Felipe

What is the main benefits of using ISL trunking?

How does exactly load balance work with and without trunking license?

Also you mentioned smart zoning before. Is there any smart zoning analog in brocade san switches?

Hello Alex.T ,

According to Brocade documentation The trunking feature optimizes the use of bandwidth by allowing a group of inter-switch links (ISLs) to merge into a single logical link....

In practice, the main benefit of trunking is that, it appears a single logical ISL, and this simplifies the routing tables inside the fabric, and most important, when there is a failure/activation of one of the ISLs, no new calculations need to be performed, and thus the traffic disruption is minimal. In the same situation, without trunking, there is a disruption until the routes are re-calculated.

When it comes to load balancing (and the use of bandwith) between switchs, it depends on the Routing policy configured on the switch. There are mainly 2 routing policies:

• Exchange-based Routing: The choice of routing path is based on the Source ID (SID), Destination ID (DID), and Fibre Channel originator exchange ID (OXID),
• Port-based Routing: The choice of routing path is based only on the incoming port and the destination domain.

Initially, when only port-based routing was available, if you had ,e.g 3 ISLs, you could have one of them heavily used whilst the other two were not used at all. In that case, trunking was very beneficial as it overtook that potential congestion situation by creating a 3-isl trunk. But since exchange-based routing was released, this situation disappeared and traffic is evenly balanced among all the ISLs. So, as far as load balance is concerned, trunking does not offer a big improvement.

If you meant the difference in load balancing withing the ISLs that form a trunk, with and without trunking licences, here there is indeed a significant difference:

• when trunking is disabled, the traffic will be balanced among the ISLs depending on the routing policy used, normally exchange-base routing, and the load will be evenly distributed among them.
• when trunking is enabled, the traffic inside the trunk won't be evenly distributed among the members: The trunk applies its own load balance algorithm and will start filling up one ISL and when it reaches certain threshold, traffic will be routed via another one, and so on if there are more than two ISLs.

Hope it answers your query.

rgds,

Felipe

Why do we need more buffer credits on ISL ports compared to normal Host/Storage Ports ?

Hi there koppuru 

Thanks for posting this question. I consider that there are 3 main reasons to have a larger number of buffer-to-buffer credits (BBC) on an ISL:

• The first one is due to the distance, the longer the ISL is the more BBC it requires to keep the link full with frames.
• The second one is that, internally, the ISL is logically divided into Virtual Channels (this only applies to Brocade switchs, Cisco switchs don't use this feature) and a certain amount of BBC is assigned to each Virtual Channel, increasing the number of required BBC to successfully work.
• Additionally,we have to bear in mind that 99.99% of the frames that go through an ISL are going to a different destination other than the ISL itself, so the ISL has to keep the received frame until it can send it to the next step in the frame journey to its destination. By assigning more BBC we can improve the behavior and performance of the ISL.

Best regards,

Felipe

Felipe,

to piggy back on koppuru questions, is there a formula how to calculate B2B credits. Anything specific for DWDM versus FCIP ?

Thanks

Felipe, hay alguna diferencia en performance cuando se usa una zona "single initiator - multiple targets" vs. "single initiator - single target"?

Gracias

it is common courtesy to post in English if you see everyone else contribute in English.

please post in English