Help with the E20-322 Exam, regarding ISL's

Hello -

We have forwarded your message to one of our curriculum managers and this might be best discussed live.

Would you please email our Proven Help Desk with your contact information so that we can coordinate a call between our curriculum manager and yourself.

Best regards,
Debi

Hi Fred...

If you click on the picture it will enlarge...if you do so it should be clear enough to read...

I think your math is wrong....due to the fact that the question specifies splitting the 4 switches into a dual fabric with 2 swithces in each fabric...

And observe the fact that the port speed is  in Gb, and the througput is in MB....

Hi Guys

did anyone come up with a final answer to this question ?

thanks

Paul

Hello Paul -

I spoke to one of our curriculum managers and he provided the following response:

Some good points were made in this thread.  For success you need to understand and blend in the following into your analysis and thinking:

1. Dual fabric topology means 2 separate fabrics without interconnection between them (else it’s a mesh which would be a single fabric).
2. With 4 independent switches to start with, that means 2 switches per fabric, with each sending its workload to its companion switch.
3. Good design should balance the workloads between each fabric (pair of switches in this case) – highest ISL load would then be ~2000MB/sec.
4. All ports run at 140Gb/sec so this must be converted to MB/sec to calculate how much capacity each ISL could support.
5. Then you calculate the minimum number of ISLs required to support that highest load.

It’s never easy to work through these sort of questions because other factors that affect workloads and utilizations ought to come into your mind too, such as:

1. Is it reasonable to assume the workloads given are (sustainable) peaks?  Or are they overall averages or just instantaneous peaks?       
2. At what maximum utilization would you plan to run those ISLs?  Certainly below 100% in practice at sustained peak loads.
3. Should you consider adding protocol overhead into the stated workloads?  Or would you expect those workload figures to include that?
4. Should you factor any workload growth into the calculations? 

Each question you encounter should be analyzed to understand what the data you’ve been given most likely means.  As with real customer situations, you sometimes have to make reasonable assumptions when there’s no additional information available to help you.

The good news for this question is that it is no longer on the practice test for the E20-322 exam, which was updated last week – see Proven Professional portal for details.  So this discussion is moot, though I hope this response helps towards a better understanding of this question and other questions in general.       

And I can't help jumping in here with a factor that doesn't seem to have been considered (although the question itself is no longer on the practice exam).If you take the original configuration as four independent switches and split them into pairs to be ISLed together... if you don't change anything else in the configuration when you do that... Almost no ISL traffic will be required at first because you are already configured for almost total locality on each of the switches. Ideally this would change over time, but but on day one the ISLs would be almost unused (except for management traffic) unless you explicitly moved devices, hosts, or host to array zoning to utilize the ISLs.

I think the true answer to this question would depend significantly on what kind of traffic was expected to traverse the ISLs in the final configuration. This is one of the challenges with creating good test questions. Getting enough info into the question to ensure that ambiguity can't invalidate what would otherwise be the correct answer. At the same time you have to avoid putting so much information in the question that it confuses the issue. I suspect in the long run that may have had something to do with this question not surviving the exam revision process :-)

This question was on the V4 ( the old) version of the test, both on the Practice test, and as a variant in the proctored tests at Pearson Vue.

all the versions of the question was pulled from this exam, as they could be answered in so many was, depending on what best pratices one took into consideration.

They have recently delivered a brand new exam, made out from the new Design Workshop V5...So this is only a historical issue...

But thanks to every one for participating.