This post is more than 5 years old
60 Posts
0
3466
October 26th, 2013 03:00
E20-326 Sym TA design - query on savedev calculations in exam
Hi,
I am just a little confused with snap % change rate. Do we always add the 15% buffer to % change rate given in the exam or not? This is important for exam questions. So in the exam if % change rate is given do we apply the 15% buffer to this for calc e.g
Question in exam calc no of save devs with 200 vdevs assuming 17% change rate?
No buffer
200 * .17 = 34 savdev
With buffer
200 * .2 (.17*1.15 rounded up) = 40 savedev
and other calcs with % change rate do we assume the buffer is built in for calcs or do we apply the buffer for every calc
In the field I would apply the buffer but for the exam I want to ensure my interpretation is correct
Your help with this is appreciated
Victor
codyhosterman
286 Posts
0
October 29th, 2013 09:00
Sorry Victor, took me a while to find the right person to answer this. This is what I was told, let me know if it helps:
"Victor’s interpretation is correct. We say in the course material that it is best practice to add 15% buffer to the calculated change rate. So the buffer should be added to the change rate given in the question. The actual question which has been quoted is straight from the course material, wherein a 15% buffer is added to the change rate of 17%. So the effective change rate used is 20% (0.17*1.15)*100 ~ rounded off to 20%."
victorforde
60 Posts
0
October 29th, 2013 09:00
Thanks to you and your colleague Cody! That is good enough for me. savedev questions involving % change would be, number of disks or the savedev capacity. I will apply the 15% buffer to % change given.
I will let you know how the exam goes in twitter land
codyhosterman
286 Posts
0
October 29th, 2013 09:00
Sure thing! Good luck with the exam!
Quincy561
1.3K Posts
1
January 14th, 2014 06:00
So that would be 12 VP Snap sessions of 300GB. I don't know what the assumption is for the change rate over the 48 hour window, but it won't be 100%, and many sessions will be able to share changed tracks on the targets. I would say that 900 or 1200 would be the correct answer.
kavuri
10 Posts
0
January 14th, 2014 07:00
Could someone explain how it 12 VP snap sessions ?
kavuri
10 Posts
0
January 14th, 2014 07:00
Thanks Quincy !
victorforde
60 Posts
1
January 14th, 2014 07:00
Hi,
I think the answer is 900GB
VP Snap requires either
1.) 2x Source and 1 x the target CAAR space for the first 16 snap sessions
or
2.) 3x source and 1 x target CAAR space for copies 17-32.
Note: Amount of CAAR is the entire capacity of dev allocated or not.
As Quincy said there are 12 VP Snap sessions so this is a.) 2 x 300GB + 1 x 300GB = 900GB
Regards,
Victor
Source ->. Symmetrix Solutions Design Course: Module 4 Lesson 2
Quincy561
1.3K Posts
0
January 14th, 2014 07:00
One snap every 4 hours, or 6 snaps for a 24 hour period. The question says two days (assume that means 48 hours) so 12 snap sessions.
victorforde
60 Posts
0
January 14th, 2014 07:00
No problem. Good luck with the exam! It is tough but all the more rewarding when you pass
victorforde
60 Posts
0
January 14th, 2014 07:00
Hi,
Brain fart there
jl is right with 12 tgt devices (corresponding to 12 VP Snap sessions) and not 1 as I had it.
Victor
dynamox
9 Legend
•
20.4K Posts
0
January 14th, 2014 08:00
why do you multiply 12 x 300 , don't VP snapshots share changed blocks ?
dynamox
9 Legend
•
20.4K Posts
0
January 14th, 2014 08:00
ahh..makes sense. Is CAAR a configurable value and what resources does it use on VMAX (cache ? )