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E20-324 FAST question

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would like to know how to go about doing this calculations for the following question thanks

customer has a heterogenous pool with the following config:

1000GiB of flash, 50 Gib free

5000Gib of SAS, 1000 Gib free

50000Gib of NL-SAS, 30000 Gib free

the customer creates a new lun with data placement policy set to "auto-tiering".  The LUN is then populated with 400Gib of data.  How is data distributed?

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C_TaylorYearns
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Re: E20-324 FAST question

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Yep, starting in Flare 32 it starts at the highest available tier then auto tiers.

You can read more about it on page 16 of the FAST VP white paper:

https://support.emc.com/docu32691_White-Paper:-EMC-FAST-VP.pdf

So to answer your inital question, 50 GB of the 400 GB would land on SSD and the remainder would land on your middle tier.

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C_TaylorYearns
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Re: E20-324 FAST question

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In Flare 32, when creating a lun with auto-tiering enabled, the data will be located on the highest available tier.  In this case, 50 GB would be on flash, and 350 GB would be on SAS drives.

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Karthik_Kallam
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Re: E20-324 FAST question

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If "auto-tiering" is enabled, data is distributed evenly. In this example 50:1000:30000=> 1:20:600

So 400GB is distributed as 0.64GB in Flash, 12.8 GB in SAS and 386.56GB in NL_SAS

Calculation:

1x+20x+600x=400GB

621x=400GB

x=400/621GB

multiply x with respected ratios

1x:20x:600x => 0.64 : 12.8 : 386.56(Approx)

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C_TaylorYearns
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Re: E20-324 FAST question

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Karthik,

It's my understanding that starting in Flare 32 it no longer distributes the data evenly as it did in previous verisons of Flare code. Would you concur?

C_TaylorYearns
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Re: E20-324 FAST question

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Yep, starting in Flare 32 it starts at the highest available tier then auto tiers.

You can read more about it on page 16 of the FAST VP white paper:

https://support.emc.com/docu32691_White-Paper:-EMC-FAST-VP.pdf

So to answer your inital question, 50 GB of the 400 GB would land on SSD and the remainder would land on your middle tier.

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8 Krypton

Re: E20-324 FAST question

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You are right as I understand too. The new recommended policy is Start High then Auto-Tier. See this video 09:10 confirming same VNX Video - FAST VP - YouTube i.e. flash first

Regards,

Victor

8 Krypton

Re: E20-324 FAST question

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flash first! You are correct.

pokus123
6 Indium

Re: E20-324 FAST question

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There were problems in few environments, if I remember well, customers who had lots of writes had a problem if tiering was enabled, because of using lowest available tier prior code 30? Not sure... And thats not a good idea using NL-SAS from pool for huge random write peaks... So now should be as it is described here - highest available tier...

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golnaz1
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Re: E20-324 FAST question

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Hi ,

I have a similar question in e20-324 , I got confused as the answer is different from what I think is correct, here is the question:

customer has a heterogenous pool with the following configuration:

1000 GiB of flash, 400 Gib free

10,000 Gib of SAS, 2,000 Gib free

80,000 Gib of NL-SAS, 20,000 Gib free

the customer creates a new lun with data placement policy set to "auto-tiering".  The LUN is then populated with 500Gib of data.  How is data distributed?

a. 300 GiB on Flash , 200 GiB on SAS , no data on NL-SAS

b. 166 GiB on Flash , 166 GiB on SAS , 167 data on NL-SAS

c. 9GiB on Flash , 100 GiB on SAS , 446 data on NL-SAS

d. 400 GiB on Flash , 100 GiB on SAS , no data on NL-SAS


The correct answer is c . But what i think is correct is the highest available first ..

Please help me for the correct answer.

Thanks,

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8 Krypton

Re: Re: E20-324 FAST question

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golnaz wrote:

c. 9GiB on Flash , 100 GiB on SAS , 446 data on NL-SAS


The answer would be "c" except that you had copied the answer down incorrectly for the SAS tier.  The values you have add up to 555 GiB

NOTE: Technically there is roughly 2% overhead for pool LUNs but they aren't testing you on this.


The answer would be (rounded up😞

9 GiB Flash

45 GiB SAS

446 GiB NL-SAS

The reason it would not be "d" is because even in VNX OE for Block v32 there are 2 separate policies:

1) Start High then Auto-Tier (recommended)

2) Auto-Tier

The question states: "Auto-Tier" only.

The math would be as follows:

1) Ratio of free space = 400:2000:20000

2) Reduce to: 1:5:50

3) Calculate:

a)1x + 5x + 50x = 500

b) 56x = 500

c) x = 8.92

4) Calculate each tier:

a) Flash  = 1x   = 9 GiB

b) SAS    = 5x   = 45 GiB

c) NL-SAS = 50x  = 446 GiB