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M0nkey_tree
1 Copper

E20-324 VNX Certification

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Hello,

I am struggling with some of the questions in the practice E20-324 tests, I have been uisng the video based course. Can anyone help and explain how to calculate the answer of this example please?

A customer wants to add a SnapView snapshot to a 600 GiB LUN. Captured data show that the LUN has an access rate of 1000 IOPs with a read/write ratio of 4:1, and 8 KiB IOs. What is the expected initial bandwidth at which data chunks will be written into the Reserved LUN Pool?

A. 12.500 MiB/s

B. 1.563 MiB/s

C. 6.250 MiB/s

D. 25.000 MiB/s

Many thanks

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andre_rossouw
2 Bronze

Re: E20-324 VNX Certification

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The SAN Copy transfer granularity is indeed 2 KiB. Bear in mind, though, that this ISC session uses a Clone as the source, and that when a clone is resynchronized, the entire extent will be seen (by ISC) as having changed, and will result in a number of COFWs taking place.

In this example, the 512 GiB source LUN causes the clone to have a granularity of 256 KiB. As the clone is resynchronized, the ISC snapshot sees the full 256 KiB changing, and performs 4 COFWs. Your task is to determine how many of those COFWs will happen in 30 minutes, and to recognize that the full 64 KiB will be copied across the link.

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Sissoko1
1 Copper

Re: E20-324 VNX Certification

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Hello I am studying for the same exam and I am in the same boat as you.  I am looking for a summary formula sheet for many of the questions that require you to know a formula and thus far I have not found anything.  If you come across anything please let me know and I will do the same.

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M0nkey_tree
1 Copper

Re: E20-324 VNX Certification

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Will do thanks. Are you using DVDs for training?

Sent from my iPad

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Sissoko1
1 Copper

Re: E20-324 VNX Certification

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Yes, I have all the PDFs that I could download fromt he pre-requisite training as well as the DVD training and the formulas on how to figure these calculations out are not intuitive to find.

wwtjoemasi
1 Copper

Re: E20-324 VNX Certification

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I just passed the 324 exam this morning and was only given 4 questions that involved the calculations (1 for COFWs, 2 for bandwidth and 1 for IOPs).

The exam has gotten easier in my opinion as I failed with a 50% last month.  I agree that the DVDs are not at all a good source for training for this (or any) EMC exam.  I just downloaded the PDFs, and read all of the material that was recommended after taking the practice exam.

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M0nkey_tree
1 Copper

Re: E20-324 VNX Certification

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Thanks, that’s reassuring to hear. I failed last month with 50% too!

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SaramiR
1 Nickel

Re: E20-324 VNX Certification

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Hello,

The answer will be 12.5MB/s as per my understanding.

When you need to calculate the BW, you must determine the number of 64KB writes.

So in case of random writes, each write is 64KB so the equation will be very simple:  BW = # of writes * 64

BW = 200 * 64 = 12800 KB/s = 12.5 MB/s

If sequential, then you have to check size of IO. If IO size < 64KB, then each 64KB will take more than 1 write.

Eg: IO size 8 KB then #of writes per 64KB chunk = 64/8 = 8 therefore, total # of 64 KB writes = # of total writes/8 (in our example # of writes is 200) then: 200/8= 25 then BW = 25 * 64

Sissoko1
1 Copper

Re: E20-324 VNX Certification

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Hello:

I managed to pass my exam during EMC World.  I believe I had 5 questions that I needed to have some sort of formula to figure it out.  I did find the formula from SaramiR very useful.  I am not sure if I was able to do some good guess work on the rest of the formula related questions or not, but I got an 88, so I am happy with the results, but I still would like to know the formulas for real work situations when I working with my customers. 

Thanks,

Najuma

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mforbes1
1 Copper

Re: E20-324 VNX Certification

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As SaramiR mentioned, and also check out h5773  has the formulas at the end and examples that the vilt left out

http://www.emc.com/collateral/hardware/white-papers/h5773-clariion-best-practices-performance-availa...

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M0nkey_tree
1 Copper

Re: E20-324 VNX Certification

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Thanks all, appreciate your help.

Regards,

Mark.

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