Fibre Channel (SAN)

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Occasional Contributor
Posts: 14
Registered: ‎06-25-2013

manual and smooth load rebalance between ISL trunks

Hi

We have two main sites. Directors are connected via dark fiber. (We are using

lw SFP-s and ISL trunking, and it is working properly.)

Now we have installed a new (second) ISL trunk

between datacentres. (The new trunk has a same bandwith and cost like the first one.)

The main traffic goes till now thru the old ISL connection. This behavior is right, because

the default is the port based routing policy and DLS is not enabled.

But we want to rebalance load between ISL trunks manuallay. Without traffic

interruption. Is there any method to achieve this goal?

Thanks in advance

Lajos

,

External Moderator
Posts: 5,034
Registered: ‎02-23-2004

Re: manual and smooth load rebalance between ISL trunks

--->>>But we want to rebalance load between ISL trunks manuallay.

if I understood your question correct:

Since the ISL is Trunking formed, they do not have Influence to balance to.

TechHelp24
Regular Contributor
Posts: 164
Registered: ‎05-11-2011

Re: manual and smooth load rebalance between ISL trunks

Hi Lajos,

as i understand you have now two ISL-Trunks, one without traffic.

Work-Around:

Disable the second unused ISL-Trunk. Enable DLS and enable trunk again.

The routes are calculated new and the traffic is balanced by the DLS-Feature. Since FOS Version 6 (i do not know the correct Sub-Version) the Feature is enhanced to Lossless-DLS. So there is only a minimal Risk that you loose one Frame.

But this can not be manually maintained.

Search for Lossless DLS on the Brocade site.

Regards

Ralf

Kind Regards
Ralf
Occasional Contributor
Posts: 14
Registered: ‎06-25-2013

Re: manual and smooth load rebalance between ISL trunks

Hi Ralf!

Unfortunately we can not switch on DLS, because we are using storage replication.

Storage replication perequisites are: 1. port based routing policy, 2. DLS disabled,

3. In Order Delivery switched on.

Second problem regarding DLS is the fimware level. Directors are running on v5.3.1a FOS,

due to some compatibility reason.

My first idea was to play with link cost. I can decrease link cost on a new ISL. But I'm worried.

First, the link cost change does not take effect immediately. (I mean, that chosen

route used when one of the devices in the fabric goes offline or the fabric changes.)

Second pain point is: the different link costs can result an asymmetric load in ISL-s.

In a week or in a month all fibre traffic will use the lower cost path.

Thanks,

Lajos

Regular Contributor
Posts: 164
Registered: ‎05-11-2011

Re: manual and smooth load rebalance between ISL trunks

Hi Lajos,

you can logout and login some of your initiators without changing the costs.

Port-Based Routing will put the traffic then with round robin towards both trunks.

But this is TA for the initiators.

Regards

Ralf

Kind Regards
Ralf
Occasional Contributor
Posts: 14
Registered: ‎06-25-2013

Re: manual and smooth load rebalance between ISL trunks

Hi Ralf,

You are absolutely right, I think.

But, if the new (unloaded) ISL will have less link cost, all new fabric login

must use the new path. By definition. So I can equalize ISL loads twice faster,

in best case. Of course, when we reach the 50-50% load share, we should restore default

link costs.

Best regards,

Lajos

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