[ Cloud Computing ] Re: why virtualization?

Dan Kearns wrote:
> On Wed, Dec 17, 2008 at 10:37 AM, Niels Goldstein
> <niels.goldstein@oracle.com <mailto:niels.goldstein@oracle.com>> wrote:
>
> Virtualization is a means to disconnect the running application from
> the underlying hardware. Its an enabling technology used by all the
> cloud computing
>
> ...etc
>
> We select servers based upon cost of CPU to Ram to Power and Space
> ratio. And that changes over time. Virtualization also gives us the
> freedom to select hardware at todays prices, and not feel locked
> into one vendor.
>
>
> So I buy some of these arguments, but by no means all. If you believe
> folks like James Hamilton, datacenter buildout at scale means you can
> reevaluate almost all your hardware assumptions without adding
> significant cost to the buildout, and with the potential of oom-sized
> operational benefits. It's hard for me to believe that current
> enterprise-focused hardware (eg blade servers, big sun or ibm boxes,
> etc) are what you'd choose.
>

I certainly think that hardware in cloud data centers will change, for
example:

1. If reliability is being handled outside the hardware, then things
like redundant PSUs may not make sense, they suck power and do little
for the overall availability of the cloud.

2. If storage is consolidated, then why have space for 6-8 drives in
each server

3. External I/O virtualization in the form of MR-IOV expansion boxes
means you don't need to put room for lots of PCI slots in the
application servers

> Virtualization (assumed to mean os virtualization) clearly can ease
> operational cost for a legacy application stack, but it is a pretty
> blunt instrument to apply to things like workload management - you're
> essentially maximizing the size of your movable state, introducing an
> incredibly coarse-grained locking infrastructure, and adding
> considerable management complexity (eg blowing out your spanning trees
> just to preserve the mac you had, because the os doesn't expect that to
> change in a single tick) in exchange for preserving your current
> architecture. That's more than just a 5% runtime penalty.

Yeah, but its dirt cheap to do and well understood and sometimes that's
enough ;-)

>
> Krishna, as I'm totally ignorant on multi-core designs - is the primary
> power-saving benefit purely a packaging issue, eg sharing a power line
> amongst the cores vs adding a whole additional "card", or is it a more
> integrated thing where there are dynamic runtime benefits derived from
> shared componentry? ie if I have an 8-core cpu in a huge datacenter
> buildout, is it equivalent to expose that thing as if it were 8 separate
> "computers" vs one 8-cpu "computer"?
>
>

Multi-core is about two things:

1. GHz walls means that we can't simply make the CPU faster every year
by bumping the clock rate. Using multiple cores in a single CPU lets you
get some benefit from naturally parallel/multi-threaded bits of code

2. Putting multiple cores in a single CPU means that you can pack an
awful lot of processing cores in a single box which is attractive for
virtualization.

That's one of the additional benefits of virtualization. Without
virtualization I've got one OS hogging all the processors and probably
not making very effective use of them regardless of whether they are
eight discrete chips or a single chip with 8 cores.
--
Nik Simpson

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