[CentOS-virt] Reading the new 6.0 manual - now questions

Fri Jun 17 20:16:18 UTC 2011
Scott Dowdle <dowdle at montanalinux.org>


----- 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.

Scott Dowdle
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