Experiences/thoughts about hardware recommendations

This is for the dbas, architects, technical pre-sales, or anyone who
has to do with recommending Servers.

Often I encounter situations where I'm expected to help the pre-sales
team to come up with a hardware recommendation that will be included
on the technical proposal for a client (well thorough scoping has
already been done).
My ex-boss came up with a capacity planning template for storage, CPU,
and RAM which can be quickly used by the Sales/Pre-Sales for hardware
recommendations and creating technical proposals.

The storage sizing part part of the template was okay. And we've been
using it for quite a while.

However, I don't completely agree on the CPU and RAM capacity
template. I think there's a more scientific way of doing it. Or I have
to say many ways of doing it.
In my opinion this could be achieved in 3 ways:

1) ROTs (Rule of thumbs)

ROTs are not applicable to all environment or to all project that
you'll have, this may not consider the workload of the system like the
batch jobs ratio to the cpu utilization and oltp ratio to the cpu
utilization. And most likely there will be vendor specific ROTs for
specific applications. So if it's comming from Oracle, and I have an
E-Business suite apps with specific ROTs that are current then I may
have to follow it. What I mean by current is, ROTs from 1990's are not
applicable today given the trend now is to go multicore.

2) Benchmarks

This is where you actually run you application on a specific hardware
with X number of CPUs. We get to see more of this at TPC.org. Oracle
together with hardware vendors from time to time publish some
statistics about the benchmark. We could infer on the results but
still may not be applicable to other applications. Still it will
depend on workload (oltp/batch) / #ofdatabases / #ofusers.

3) Models

Models are very useful if you can't afford to make benchmarks. But you
could also model data comming from benchmarks which is far better
because you could use the math for you to see the future. I've read on
a book where Oracle Performance engineers use ratio modeling for quick
estimate on CPU requirements. Linear regression could be useful to
know when you will run out of gas, I mean, when will be the limit of a
certain resource. And don't forget, that there's a concept of
effective CPUs where you have X number of CPUs let's say 12 but you
are not actually maximizing it and you're just able to use 6 because
of some factors which could be coherence, contention, concurrency. So
even if you add 20 more CPUs don't expect that your application's
performance will be linear to your CPU power. Well this may sound all
theoretical, but some people are already working on these models.


So What I'm trying to say here?
Well, on my part... I may have to research/learn more on this area, but...

- I don't like the feeling of being on a project where I ask the
project manager how did they came up with the hardware specs, and he
only says.. "the winning bidder came up with it.." then you find out
sooner after setting up everything that the hardware is either
overpowered or underpowered.
- I don't like the feeling of guessing or just giving something for
the sake of coming up with a hardware recommendation and technical
proposal

So I have to ask good people, & people in user groups, or people with
similar roles, how they do it?...how you do it?

I hope we could build up on each others ideas regarding this area of
performance :)  (And I hope I made you curious about it..)

Share your experiences/thoughts about it.. :)





- Karl Arao
http://karlarao.wordpress.com
--
http://www.freelists.org/webpage/oracle-l


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