Re: VM Host Hardware Recommendations.

Large CPU cache is relative to small CPU cache. ;)

Here's an example, looking at i7 CPUs...

http://en.wikipedia.org/wiki/Intel_Core#Core_i7

http://en.wikipedia.org/wiki/Intel_Core#Core_i7_2

So, if you're going to stick within the i7 product lineup, well... you
only have a few choices for L3 cache.

Further, you often have only one choice, or no choice to make, dependant
upon the number of cores you choose.  Taking a look at current i7 CPUs,
you don't even have a cache choice if you plan to go 4 core...

You did with older i7 variants, however... 

Of course, everything has its price, and that is another consideration.
If moving from a 6MB to 8MB cache doubles the price of the CPU, it may
then not be worth it.  It is all about price point versus power.

I'd certainly pay more for larger cache though, Bart isn't off base
there... 

 


On Thu, 28 Jul 2011 21:21:15 -0400
Garth Boyd <[email protected]> wrote:

> Question about CPU cache:
> 
> Can you quantify what "large CPU cache" would be?
> 
> Thanks
> G
> 
> 
> 
> On 26 July 2011 09:37, Bart Trojanowski <[email protected]> wrote:
> 
> > First and foremost you need a CPU with hardware virtualization
> > extensions. I am taking this for granted because it's hard to find a
> > server class CPU w/o this.
> >
> > As Brad pointed out, it's hard to give specific advice until you know
> > the I/O vs CPU vs memory load.  However, I can give you some general
> > advice.
> >
> > There are three things I look for when building hosts for
> > virtualization:
> >
> > - cache
> >
> > Having a large CPU cache means that context switches (in this case
> > from one VM to another) are not as costly.  It also reduces the
> > contention on the memory bus, which is a shared between multiple VMs.
> >
> > - RAM
> >
> > Naturally more RAM allows you run more VMs... but more importantly
> > having lots of RAM prevents the need to go to disk to get data as it
> > can be cached.  Having free RAM around can improve certain kind of
> > disk I/O loads.  This is true on non-virtualized systems as well.
> >
> > - cores
> >
> > If you have a lot of active VMs, the system will spend a lot of time
> > ushering VMs in and out of the CPU.  This wastes time, and having more
> > cores helps.  Be careful here... adding cores without adding to the
> > CPU cache can make things worse.
> >
> > After these, thing get expensive.  You can pin dedicated network cards
> > to each VM to improve network I/O.  You can also improve your storage
> > I/O bandwidth by using a SAN.
> >
> > -Bart
> > --
> > OCLUG general discussion list
> > [email protected]
> > http://oclug.on.ca/mailman/listinfo/oclug
> >
> 
> 
> 
> -- 
> - Garth
> -- 
> OCLUG general discussion list
> [email protected]
> http://oclug.on.ca/mailman/listinfo/oclug
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