GiB and KiB Vs GB and KB

Hi Gene

Good to hear, now that we have opened this can of Worms, have somenone look into the modules on Exchange SQL and Oracle for the Expert level VNX exams.

The materials are full of references to very old data.

73 and 146 Gb disk

Sata and FC disk's

Iops per drive that differs to what is shown in the student guide to the VNX performance workshop ( SSD ROT 2500)

Flare 24 

And so on.

It look like somebody tookthe modules from a Clariion clase and rebranded them as a VNX paper....

This fact makes it very difficult to do the Math when trying to pass your Expert level exams....

in effect you may have to do the numbers 8 times due to these small errors.

Jim,

Thanks for bringing this to our attention. We will check into this right away on both the exams and practice tests to be sure that the terms are being appropriately used, and will promptly make any changes that are required.

Gene

So far nothing has come of this.

And the matters got worse for some of the Expert level exams you do not have a calculator available to help with the math.so now we are not only testing your knowlegde but also your math skills..

Byt for your math the following goes wrong,

The logging is done with 8 KiB IOPS. So the math is

25 GiB / 8 KiB / 8 hours ( in seconds)

1024*1024*1024*25 / 8192 / 28800 = 113,77 IOPS

And my guess is that you are correct in assuming that you have to multiply taht answer by 2 to get the Write penalty for R1/0 into account.

So what is the outcome of this question?

I think 25GB worth of transaction logging at 4kB per I/O means that 25,000,000,000 / 4,000 = 6,250,000 I/Os per day, which is 6,250,000 / 86,400 per second --> 72.33 IOps. Since this is DAS based and the Storage on tha VNX is RAID10 you should multiply by 2, so the number of transaction IOps is 144.66.

If I say that 25GB is actually 25GiB then the math is this:26,843,545,600 / 4,096 = 6,553,600 I/Os per day, which is 6,553,600 / 86,400 = 75.85 IOps. Times two for the write penalty still makes a little more then 150.

Where did I go wrong?

Ah, I see it's an 8 hour business day, but that would devide the answers by 3 making them 48 and 50, which still doesn't come close to the lowest number of the 4 answers

hahaha, thank you for helping out there. I was writing 2 posts at the same time and I didn't spot my error !

Btw: take a look at the "Ask the Expert" session I'm doing right now: https://community.emc.com/events/1465 and https://community.emc.com/message/652424

In your first attempt you end up with the correct amount of data, but that you divide by a number that is to small in a factor of 2, the result you then divide by the numbers of seconds in a day, that is three times to big.

If you take your 75.85 IOPS and divide by 2 and multiply by three you have the correct answer...before Raid penalty

RRR wrote: So what is the outcome of this question? I think 25GB worth of transaction logging at 4kB per I/O means that 25,000,000,000 / 4,000 = 6,250,000 I/Os per day, which is 6,250,000 / 86,400 per second --> 72.33 IOps. Since this is DAS based and the Storage on tha VNX is RAID10 you should multiply by 2, so the number of transaction IOps is 144.66. If I say that 25GB is actually 25GiB then the math is this:26,843,545,600 / 4,096 = 6,553,600 I/Os per day, which is 6,553,600 / 86,400 = 75.85 IOps. Times two for the write penalty still makes a little more then 150. Where did I go wrong? Ah, I see it's an 8 hour business day, but that would devide the answers by 3 making them 48 and 50, which still doesn't come close to the lowest number of the 4 answers

Hmmmm.... I'm still trying to wrap my mind about this. Where did I go wrong, besides the 8kiB thing?

1) 25,000,000,000 / 8,000 = 3,125,000 I/Os per 8 hours (86,400 / 3) = 108.5 IOps

2) 26,843,545,600 / 8,192 = 3,276,800 I/Os per 8 hours (86,400 / 3) = 113.78 IOps

So based on the fact that it all should be in GiB outcome number 2 is the correct one and designing a VNX RAID10 solution the number of IOps the transaction log VNX LUN has to be able to handle is 113.78 x 2 = 227.54

Ah, about the 8kiB I didn't know, but that doesn't explain my outcome.... Oh well, must be the Windows calc.exe then

I'm sorry, other than what I posted I don't know much about iSCSI. I was hoping for some help too, but nobody came to the rescue... yet.

Hi RRR

I have already seen the Ask the Experts topic, and was hoping that someone can give some good info on my ISCSI question.

Yeah correct: converting "front end" IOps to "back end" IOps

The write penalty is only important when you're converting LUN IOPs to disk IOPs. In this question, since it referes to LUN I/O, the RAID type doesn't matter.