[HCoop-Discuss] Dedicated servers?

[Ron Senykoff]

On Thu, May 21, 2009 at 3:07 PM, Adam Chlipala <adamc at hcoop.net> wrote:
> These are some good reasons.
>
> Ron Senykoff wrote:
>> - You can have a standard base image that you install for any new VM.
>> Basically a prebuilt lean VM waiting for you to install whatever
>> software you want.
>>
>
> Can't we achieve that for real machines, too, with regular disk images
> and some way of getting them onto machines?  There must be standard grub
> kind of tools that facilitate that.
>

Sure, you could do it with a regular machine too.

>> - It becomes much easier to isolate which application (mysql, mail,
>> etc) is causing load on the system. With multiple physical servers in
>> place, you can move the VMs around as appropriate to best distribute
>> the load. This allows for real optimization of your hardware
>> utilization.
>>
>
> This also forces you to figure out ahead of time what resources to
> allocate to each VM, right?  If you got it wrong, do you need manual
> action to keep one VM from being resource-starved even when there are
> free resources available?

I'm not sure about Xen, but VMWare provides for dynamic resource
allocation. So, there's way less intervention than say, installing
more RAM or a faster CPU. VMWare can even migrate the VMs on the fly
to another machine that has less utilization, without intervention.

> As for other disadvantages of virtualization, I can think of a few:
> Initial set-up overhead (labor-wise) is higher.

At which stage? Setting up a new virtual server, especially if you
have already built a server image to start from, is almost trivial.
Setting up Xen however definitely adds that additional layer of
complexity.

>For fully-utilized
> machines, you can handle less load with virtualization than otherwise.
Depending on the route you go, the overhead with Xen can easily be
~3%. Also, in the end most virtualized environments see much more
efficient use of their hardware as there are no dedicated servers
sitting there running something that is hardly ever used.

> Some software/hardware may work oddly with VMs.
Examples? I have seen one case where VM was an issue, and this was
with Asterisk (voip server). However Asterisk has some hard real-time
requirements because it's doing live audio processing. Many people do
run it in VMs however, without any problems. They do however use a VM
optimized kernel which I believe also includes the real-time kernel
patches.

Anyways, I don't really have the time to discuss what is good or bad
about virtualization in general. That can be found on google
anyways... My question is does it make sense for Hcoop?

Cheers,
-Ron