[OT] Virtualization (WAS: UNIX V7)

[Liam Proven]

2009/6/12 Pontus Pihlgren <pontus at update.uu.se>:
> On Fri, Jun 12, 2009 at 03:51:18PM +0100, Liam Proven wrote:

> <snip>
>> great servers running all those as guests, you *still* have 50 copies
>> of Windows to maintain. The work level doesn't drop much at all - you
>> just save space and electricity.
> </snip>
>
> This was my point, the work level doesn't drop, but it certainly does
> not increase!

True.

>> And even that is a partly illusory saving, because much of the power
>> and resources that a computer will use in its typical working life of
>> a few years is spent in building the thing. So by replacing multiple
>> working hardware boxes with a single big new machine to run the same
>> workloads, you're wasting all that sunk-cost of the manufacture of
>> those boxes, while "spending" a load more non-recoverable resources
>> that were used to make the new box.
>
> Well that all depends on the load. Recently we moved two low-load
> machines into a virtual environment, perhaps we didn't cut the
> power/cooling costs in half, but it's certainly an improvement.

Good point!

>> Let's say you're running 4 copies of Windows, in VMs, on a host copy
>> of Windows. That's 5 gig of RAM and 4,500MHz of CPU bandwidth blown on
>> all those copies of Windows, of which 4.5GB and 4000MHz are running
>> duplicated code that is shared by all the VMs.
>
> In this case I agree that virtualization is probably a bad idea. But if
> the client OS needs 250MB worth of memory and a few percent of the CPU.
> You could easily squeeze three of them into 1GB (asuming the host OS
> needs only 250 MB, which might be optimistic). Also think of the case
> where the client systems doesn't need the CPU all the time.

Even so, it's more efficient with OS-level virtualisation. The only
case I can see for full-function OSs running on top of other
full-function OSs is, for example, if you want 1 host to run several
different OSs - e.g., a VM with NT4 Server, a VM with Linux and a VM
with Solaris, or some random combination such as that.

However, I fear that the most common reason will be that all the
techies know is Windows Server, so they just run lots of instances of
that and waste masses of resources.

Even if you have the resources to burn, waste is bad. Waste is always
bad, I feel.


>> If, instead, you were running an OS that could partition itself so
>> that the 4 workloads all ran on the same shared kernel, but completely
>> isolated from one another, so that one could have one version of the
>> core libraries and another a different version,
>
> This would be awsome, is there any such system?

Several. Solaris with Containers and Zones & FreeBSD with Jails are
the 2 best-known. AIX has WPARs, which I believe are similar. Linux
doesn't have anything built into the kernel, but there are a number of
3rd party additions: FreeVPS, Linux VServers & OpenVZ.

Virtuozzo is a commercial product for doing much the same and is
available on Linux and Windows.

> My guess is that it is
> very hard to get right.

I think it's easier when it's built into the OS than to add it on later.

> However you totally miss the case where you need
> different operating systems.

I hadn't read this when I wrote the earlier part of my message, honest! :¬)

>> Does that make my point clear?
>
> Yes, I see that there are cases where virtualization is really stupid.
> But I hope that my argumentation for the cases where it is smart make
> sense :)

Oh, it certainly has its uses, and on VMware's ESX server, tools like
VMotion and VirtualCentre are a massive boon for manageability, albeit
at a small but significant price in terms of performance. But
performance is rarely a problem these days.

It just bothers my sense of systems elegance to see big full-function
OSs running on top of other big full-function OSs. I really deeply
dislike that sort of kludge, and my suspicion tends to be that an
inelegant solution is a flawed solution and that those flaws will
eventually come back to bite you.

-- 
Liam Proven • Profile: http://www.linkedin.com/in/liamproven
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