CentOS virt - Jun 2011 - Reading the new 6.0 manual - now questions

I'm new to running VMs, so I'm hoping this hasn't been a problem 
question asked before. I've only glazed over the emails from this list 
since I've joined due to not really needing all of the great information 
if provides.

Eric suggested I wait for Centos 6 to start loading my new VM host, and 
so I grabbed the RH Virtualization PDF and started digging in.

Firstly, it occurred to me that Centos 6 might not provide the 
virtualization rpms like it did with Centos 5. RH makes this an add-on 
to their license. Does anyone know if the upcoming Centos 6 will provide 
the virtualization packages (right away or in the future)?

Secondly, I'm not sure I understand the CPU allocation stuff. If I have 
6 cores, it appears I can only create VMs that use 6 cores total. Using 
the GUI for creating a new VM will provide me with a max number I can 
allocate. Does this mean that I can allocate, for example,  3 VMs that 
use 2 cores each and never be able to create any other new VMs or does 
this mean I can create as many VMs as I want but only start VMs  that 
use the max total cores or less?

I should get my shiny new machine next week, the one with real 
virtualization capability,  so some of this may be answered on my own by 
playing around, but until then, thought I'd get a head start on 
rectifying my stupidity.

Thanks for any help (along with a special thanks to Eric for his 
original help).

steve campbell

Hi Steve,

Le 17/06/2011 17:22, Steve Campbell a ?crit :
> Firstly, it occurred to me that Centos 6 might not provide the
> virtualization rpms like it did with Centos 5. RH makes this an add-on
> to their license. Does anyone know if the upcoming Centos 6 will provide
> the virtualization packages (right away or in the future)?
I installed SL 6.0 on one of my machines, and indeed it provides KVM 
(Description in French):
# yum groupinfo virtualization
Loaded plugins: refresh-packagekit
Setting up Group Process
epel/group_gz
| 201 kB     00:00

Group: Virtualisation
  Description: Fournit un environnement afin d'h?berger des clients 
virtuels.
  Mandatory Packages:
    qemu-kvm
  Optional Packages:
    qemu-kvm-tools

I think CentOS will do the same for 6.0.
> Secondly, I'm not sure I understand the CPU allocation stuff. If I have
> 6 cores, it appears I can only create VMs that use 6 cores total. Using
> the GUI for creating a new VM will provide me with a max number I can
> allocate. Does this mean that I can allocate, for example,  3 VMs that
> use 2 cores each and never be able to create any other new VMs or does
> this mean I can create as many VMs as I want but only start VMs  that
> use the max total cores or less?
You can assign multiple VMs to one CPU. For example, you can have a 
hostmachine with dual-CPUs quadcore, and have 15 VMs or more installed 
on it, and some of them assigned with two cores or more. It is only more 
threads on a core.

Alain

-- 
=========================================================Alain P?an - LPP/CNRS
Administrateur Syst?me/R?seau
Laboratoire de Physique des Plasmas - UMR 7648
Observatoire de Saint-Maur
4, av de Neptune, Bat. A
94100 Saint-Maur des Foss?s
Tel : 01-45-11-42-39 - Fax : 01-48-89-44-33
==========================================================

On 06/17/2011 05:22 PM, Steve Campbell wrote:
> I'm new to running VMs, so I'm hoping this hasn't been a
problem
> question asked before. I've only glazed over the emails from this list
> since I've joined due to not really needing all of the great
information
> if provides.
>
> Eric suggested I wait for Centos 6 to start loading my new VM host, and
> so I grabbed the RH Virtualization PDF and started digging in.
>
> Firstly, it occurred to me that Centos 6 might not provide the
> virtualization rpms like it did with Centos 5. RH makes this an add-on
> to their license. Does anyone know if the upcoming Centos 6 will provide
> the virtualization packages (right away or in the future)?
As far as I understand it these add-ons are all open-source and the RH 
packaging deals more with product support on the RHEL side rather than 
trying to "hide" something. So all these add-ons should be available
in
some form in Centos although I haven't checked the details. KVM is 
available definitely though.
> Secondly, I'm not sure I understand the CPU allocation stuff. If I have
> 6 cores, it appears I can only create VMs that use 6 cores total. Using
> the GUI for creating a new VM will provide me with a max number I can
> allocate. Does this mean that I can allocate, for example,  3 VMs that
> use 2 cores each and never be able to create any other new VMs or does
> this mean I can create as many VMs as I want but only start VMs  that
> use the max total cores or less?
If you have 6 cores available in the machine that means you can only 
allocate a maximum of 6 cores for one individual VM but you can have as 
many VMs as you like.
That means you can create 10 VMs with 6 cores each but you have to keep in 
mind that this means the VMs will be fighting over the 6 physical cores in 
the machine. Basically every time a VM schedules a process to run the host 
needs to find a physical core to run it on or wait until one gets freed up.

In other words: You can over-commit cores but you have to take care that in 
terms of actual work load you don't exceed the actual phyical capacity of 
the system.
> I should get my shiny new machine next week, the one with real
> virtualization capability,  so some of this may be answered on my own by
> playing around, but until then, thought I'd get a head start on
> rectifying my stupidity.
There's nothing stupid about it. The virtualization space is developing 
rapidly right now and what might have been true yesterday in terms of 
features might no longer be true today. Since Centos uses libvirt for 
virtualization you can pay attention to the libvirt mailing list to stay up 
to date with what's going on:
https://www.redhat.com/archives/libvir-list/

Regards,
   Dennis

Greetings,

----- Original Message -----
> RH makes this an add-on to their license. Does anyone know if the upcoming 
> Centos 6 will provide the virtualization packages (right away or in the
future)?
Just to clarify... Red Hat's virtualization entitlement is for
management/support from RHN.  The way they sell RHEL... you can have 1 VM, 4 VMs
or unlimited VMs.  When I say VMs there I mean supported RHN subscribed RHEL
installs where you register them with RHN and they get updates like any RHEL box
would.  So you are affectively getting 2, 5 or unlimited RHEL update
entitlements.  This is done by installing an additional package or two in the
RHEL VM, and registering it with RHN so it knows it is a VM and RHN knows which
physical host it is associated with.

If you want to run any number of virtual non-RHEL OSes, go for it.  They are not
accounted for.  The only thing accounted for are RHN subscriptions by physical
or virtual machines. It isn't like virt-manager phones home... it does not.

None of that entitlement stuff applies to the free RHEL clones so it isn't
an issue.
> Secondly, I'm not sure I understand the CPU allocation stuff. If I
> have 6 cores, it appears I can only create VMs that use 6 cores total.
It is my understanding that you can allocate basically all of the vcpus you
want... the only rule though is that you can't assign more vcpus to a single
VM than you have physical cpus as the OS sees them.  So if you have two
quad-core CPUs and they can do multiple threads per core... just look at
/proc/cpuinfo to see how many cpus are listed there.  It is probably the total
number of threads times the total number of cores per CPU times the number of
CPUs.  You can't go over that number of vcpus in a single VM.

So if /proc/cpuinfo on the physical host shows 16 CPUs you could make x number
of VMs with 16 or less vcpus each.  It doesn't matter what the total number
is across VMs.
>From a performance stand point some might want to allocate only as many
vcpus as they have physical cores or cpus and then pin them so they get a 1-to-1
allocation... but for most folks, as long as their hardware isn't bogged
down too much, it is a freeforall.:)
That's my understanding anyway.

TYL,
-- 
Scott Dowdle
704 Church Street
Belgrade, MT 59714
(406)388-0827 [home]
(406)994-3931 [work]