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)

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?

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

flash first! You are correct.

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...

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,

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

Thank you Christopher Imes for your complete answer .

No problem.  Unfortunately though I'm struggling to calculate the other question you posted.

Hi Christopher Imes,

so here is the question for  "highest available" . Appreciate if you can help with that.

A customer has a heterogeneous pool with the

following configuration:

-800 GiB of Flash, with 300 GiB free

-12,000 GiB of SAS, with 2,000 GiB free

-50,000 GiB of NL-SAS, with 25,000 GiB free

The customer creates a new LUN with data placement policy set to "highest available tier". The LUN is

then populated with 600 GiB of data.

How is that data distributed (numbers are approximate)?

A. 220 GiB on Flash, 380 GiB on SAS, no data on NL-SAS

B. 300 GiB on Flash, 400 GiB on SAS, no data on NL-SAS

C. 200 GiB on Flash, 200 GiB on SAS, 200 GiB on NL-SAS

D. 10 GiB on Flash, 110 GiB on SAS, 480 GiB on NL-SAS

The answer is A.

The question is testing you on whether or not you know that the system will (try to) maintain 10% free per tier.

The calculations will be:

1) 800 GiB * .10 = 80 GiB (10% of Flash will be kept free in this example)

2) 300 GiB - 80 GiB = 220 GiB on Flash

3) 600 GiB - 220 GiB = 380 GiB on SAS

Thank you for your help!