Difference between KVM and RHEV/OVIRT

Does the subject make any sense ? hmmmm.. I dont know .. It is upto your decision, because this is one of the question which I get normally from people when they hear about RHEV or if you explain about it ..

I will try to put these components in simple terms, if I fail, poke me with your comments..

KVM is a hypervisor , well yeah.. strictly speaking I have to tell that, kvm makes/turns a linux system as a hypervisor.. Thus allows you to run virtual machines inside it.. Oh.. yeah.. I have heard that .. but then what is ‘libvirt’?

libvirt is an API which allows you to talk with your hypervisor..  The applications like ‘virt-manager’ can take help from libvirt to talk to the hypervisor ( ex: kvm) .. Thus manage virtual machine..

From above, you understood that, if you have a linux kernel running in your machine KVM can host VMs and applications like ‘virt-manager’ can be used to administer it..

Then, how RHEV is related to KVM ? well, if you view a RHEV environment in your mind, it would look like this.

[ Hypervisor 1]  <———->      [ RHEV-Manager]    <———>  [ Hypervisor 2]

^                                                                                                              ^

|                                                                                                                 |

|                                                                                                                 |

|_________________________________________________________________|

Very bad ascii art ? I feel so.. nm 🙂

How this hypervisors are made ? again KVM makes this hypervisor .. These hypervisors contact/talk to RHEV-Manager server..  What is the communication channel between these hypervisors and RHEV-manager? It is a service called “vdsm”  Ok.. sounds good.. In that case , no “libvirt” ? hmmm.. RHEV2 setup was not using ‘libvirt’ in RHEV hypervisor, but RHEV3* make use of libvirt service.. In RHEV3 context “vdsm” , trigger libvirt for VM life cycle operations.. but still, vdsm is the communication agent between rhev hypervisor and RHEV-M..

 

RHEV hypervisor can be a RHEL system with kvm modules loaded.. Otherwise a ‘live CD’ image called RHEV-H can act as a hypervisor.. RHEV-H does not differ from a RHEL hypervisor in terms of kvm or vdsm.. Just think RHEV-H as a live CD image with minimal size.   It is a dedicated appliance and not supposed to run other applications like RHEL hypervisor.

We talked about RHEV-Manager Or RHEV-M , but what is it ?

In simple terms, it is the managing server.. Think of it in terms of a  ‘administration’ server.. In fact a GUI installed server 🙂

Finally, Do you want a  ‘windows server’ in a RHEV environment ? hmmm.. RHEV-Manager in RHEV 2  required it., but latest version of RHEV-3 does not require ‘windows’ server . You can install RHEV 3 Manager in a linux system with a simple command , #rhev-m setup

 

I am stopping here.. but please feel free to ask your queries , if any.. I would try to explain it in detail.. This is a simple wrap up on KVM and RHEV…

 

* MODIFIED THIS ARTICLE FOR INCLUDING RHEV 3 BITS

 

 

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