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2 Bronze

## E20-324 FAST question

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?

1 Solution

Accepted Solutions
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2 Bronze

## Re: E20-324 FAST question

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.

14 Replies
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2 Bronze

## Re: E20-324 FAST question

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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2 Bronze

## Re: E20-324 FAST question

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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2 Bronze

## Re: E20-324 FAST question

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?

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3 Silver

## Re: E20-324 FAST question

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

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6 Indium

## Re: E20-324 FAST question

flash first! You are correct.

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2 Bronze

## Re: E20-324 FAST question

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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2 Bronze

## Re: E20-324 FAST question

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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2 Bronze

## Re: E20-324 FAST question

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 ..

Thanks,

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4 Ruthenium

## Re: Re: E20-324 FAST question

 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 upðŸ˜ž

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