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# EMC E20-885 mirrorview resynchronization calculation

Hi, i need help with this question, i´ll explain my procedure to calculate it and let me know if i´m wrong:

A customer has two sites with a VNX system at each site. The local site has four application LUNs of 512 GB each. They are replicating to a remote site with MirrorView/S. The link between the sites has an effective bandwith of 100 MBPS. The application generates 1000 random IOPS of 4 MB with 3:1 R/W ratio of the LUNs. The link fails for five minutes.

How much data is copied to the secondary LUN as part of the resynchronization process?

- 4.6GB
**18.3GB**- 36.8GB
- 73.2GB

First i look for the size of the Lun is 512GB so the track size is 256KB

The aplication generate 1000 random iops 3:1 so 250 iops are for writes

They mention that are 4 luns so 256KB * 4 = 1024KB

1024KB*250iops=256000KB/s / 1024= 250MB/s

The link between the sites is 100MBPS so there is a bottleneck here, each lun can use a bandwith of 62.5 MBPS.

So if i work with only one lun the answer will be 62.5 MBPS*(5min*60sec) = 18750MB/1024=**18.3GB**

is this correct?

andre_rossouw

62 Posts

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May 18th, 2015 13:00

The question contains a fair amount of data that you won't need as part of your calculation.

Things you need to know: there are 4 identical LUNs of size 512 GB each, and the extent size is therefore 256 kB. [Note that the question would be very different if the LUNs had different sizes].

The total workload is 1000 IOPs, with a 3:1 R/W ratio, so that's 250 writes/s. Each write marks an extent as dirty, so the total amount of data on the dirty extents [and therefore the total amount of synchronization data that crosses the link] is 250 writes/s x 256 kB/write x 5 minutes x 60 seconds/minute = 19,200,000 kB / 1024 = 18,750 MB / 1024 = 18.3 GB.

The link speed is only important if you need to calculate how long it would take to perform the synchronization, or, in MV/A environments, what the upper limit of unique writes/s on the primary LUNs would be.

jony_pi

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May 18th, 2015 13:00

Thanks for the explanation

jony_pi

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May 19th, 2015 13:00

Ok Thanks

andre_rossouw

62 Posts

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May 19th, 2015 13:00

The question says that the stated load is generated

on each of the LUNs. You need to multiply your answer by 3.jony_pi

7 Posts

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May 19th, 2015 13:00

Look at this question from the practice test:

A customer has two sites with a VNX system at each site. The local site has three application LUNs of 128 GB each. They are replicated to the remote site with MirrorView/S. The link between the sites has an effective bandwidth of 100 MB/s. The application generates 800 random IOPS of 4 kB with a 4:1 R/W ratio on each of the LUNs. The link fails for 10 minutes.

How much data is copied to the secondary LUNs as part of the resynchronization process?

5.9GB

8.8GB

17.6GB

35.2GB

____________________________________________

3 LUN 128GB so 128KB Extend Size (im not sure about this)

800 random IOPS of 4KB with R/W 4:1 Write IOPS: 160 IOPS (Not sure again)

Data=160*128*10*60=12288000/1024=12000/1024=

11.72GBWhere is my mistake?

andre_rossouw

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May 20th, 2015 10:00

In the

firstquestion, thetotalnumber of I/Os is mentioned. In the second, it's the I/Oper LUN, so you need to multiply by three.jony_pi

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May 20th, 2015 10:00

Hi Andre

One last question, why in the first question where: The local site has four application LUNs of 512 GB each. The answer is only using the 256KB extend size from one Lun.

And in the second question where: The local site has three application LUNs of 128 GB each. You said i have to multiply by 3 the answer

Why one is mutiplied by the quantity of Luns and the other no?