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 écrit :
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'héberger 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
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,
(off topic)
On Jun 17, 2011, at 1:16 PM, Scott Dowdle wrote:
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.
While I suspect that yes, the system won't stop you from doing this, I did hear from a Red Hat account manager when I was pricing out RHEL that you are supposed to purchase for the total number of guests of any operating system, not just RHEL.
Or maybe I was misinformed. Anybody else familiar with this?
Eric
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Alain Péan -
Dennis Jacobfeuerborn -
Eric Searcy -
Scott Dowdle -
Steve Campbell