# XEN (HVM) vs. KVM



## wlanboy (May 17, 2013)

I have a question regarding two different types of virtualization. For our current project we did come to an agreement that we do not want to use paravirtualization. No modification of the kernel, etc.

Reading about devs running away of XEN and joining the KVM band wagon I am not sure that we should use XEN. But who cares about dev drama?

So what is the difference between XEN and KVM? The main pros/cons?


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## Ash (May 17, 2013)

Well it all depends, when you say XEN do you mean HVM or PV, im gathering you mean HVM since that's the only technology which can be compared with KVM.

HVM and KVM operate in the same way, but from what i have seen in terms of benchmarks and testing, KVM has slightly less overhead and offers closer to native performance. There was a really good document regarding KVM/HVM comparison which I'm trying to dig out for you..


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## wlanboy (May 17, 2013)

Yes I mean HVM (see thread title).

And thank you for searching the document. Looking forward to it.


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## dominicl (May 17, 2013)

I would recommend KVM for the reasons Zach stated.


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## weservit (May 17, 2013)

We are using both, Xen and KVM. New nodes will be KVM for sure. With KVM we don't see any performance loss, performance in the VM with the virtio drivers is the same as on the host node. Performance on our KVM VPS servers is better than the Xen servers. Also the fact that we can use a non modified kernel is something we like.


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## xBytez (May 17, 2013)

Preferably KVM, I personally like it more, becuase it looks like out of experience more perfomance


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## PwnyExpress (May 17, 2013)

From a security point of view, Xen probably has the better design as EVERYBODY running off that node is a guest....

However because since everybody is a guest there are going to be some performance penalties as if I get it right, everything has to go through a Virtualized bus. Personally I've only worked with Xen for quite a short time, so most of the basic fundamentals that I'm talking about here comes from Hyper-V. Somebody correct me if I'm wrong on the aspect that all Xen domains have to talk through what Microsoft calls it as a VMBus.

KVM on the other hand probably might not have the best secure design as... well the hypervisor resides inside the kernel... So if you can break that hypervisor it's game over. From what I can comprehend, KVM is the kinda the "open sourced" version of VMware if you kinda get what I mean here


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## wlanboy (May 18, 2013)

Yes VMWare Workstation, KVM, Virtualbox, Dosbox are quite the same. Mostly based on QEMU.

Hypervisors like VMWare ESX or XEN do run a master (dom0) which is providing the drivers for the hardware. Each guest does have virtual drivers which are looping back to the "master driver". Something they call "VMBus".

The KVM project might look cooler, because it is officially supported in Linux as it is a Linux kernel modification, while Xen and ESX are separate operating systems.

I will jump into the KVM band wagon. It might be easier to have the same (QEMU) hardware on all VMs.


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## Enterprisevpssolutions (May 23, 2013)

Kvm is newer, they all have pros and cons depending on what you want to use it for I prefer KVM as its easier to manage and depending on the disk type you're using easier to convert to a different virtualization platform or back to a physical system.

quick comparison and some more info.

http://www.proxmox.com/proxmox-ve/comparison

http://blog.xen.org/index.php/2011/11/29/baremetal-vs-xen-vs-kvm-redux/

http://www.vmware.com/virtualization/advantages/robust/architectures.html


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## mikho (May 23, 2013)

Have you looked at vmware?

If you are not going to sell the vm's to customers, you could go for their free version.


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## Enterprisevpssolutions (May 23, 2013)

vmware is great for the advance users but for beginners I recommend proxmox as its easy to install and configure and its free for full version. As some people that use mac don't have the vsphere option. Proxmox uses web UI and cmd which make it more compatible with all mac linux or windows.  B)


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## VPSDATABASE (May 26, 2013)

KVM and even my customers said our KVM node is better.

Same type of dedicated servers and all setup.

And KVM performed better.


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## AnthonySmith (May 26, 2013)

KVM has better performance in general however is a lot heavier on node resource so with KVM once your host node gets to around 70 - 80% full everything suffers.

HVM as of Xen 4.1.x is almost as fast as KVM however where Xen shines over KVM is that if you have 30GB you can use it and the performance of the whole node will not suffer, it is much more stable in terms of capacity.

KVM is better for performance when it comes to windows, no doubt, for linux I would still choose HVM especially now Xen is being brought back in RHEL 7.


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## fileMEDIA (May 26, 2013)

I think both are very stable, but the handling for provider is easier by using kvm than xen. You can use any kernel and don


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## concerto49 (May 26, 2013)

AnthonySmith said:


> KVM has better performance in general however is a lot heavier on node resource so with KVM once your host node gets to around 70 - 80% full everything suffers.
> 
> HVM as of Xen 4.1.x is almost as fast as KVM however where Xen shines over KVM is that if you have 30GB you can use it and the performance of the whole node will not suffer, it is much more stable in terms of capacity.
> 
> KVM is better for performance when it comes to windows, no doubt, for linux I would still choose HVM especially now Xen is being brought back in RHEL 7.


Hopefully RHEL 7 will be out soon to level the playing field. Most non-advanced people I've seen try to install XEN on RHEL 6 and fail since it's not there out of the box.


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## willie (May 27, 2013)

All the big hosting places (EC2, Rackspace, etc.) seem to use Xen.  I don't know why. OpenStack may be Xen specific.

I know where I work we use Virtualbox for some of our stuff.  I'm not sure whether that's based off Xen or what.

Xen PV has some cool clients called Unikernels that let you run applications in some languages with no OS (language runtime talks directly to the hypervisor).  That may not be relevant to your purposes though.

There's a slashdot thread right now comparing virtualization schemes, with some fairly knowledgeable commenters:

http://ask.slashdot.org/story/13/05/26/1813216/ask-slashdot-which-100-user-virtualization-solution-should-i-use


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## AnthonySmith (May 27, 2013)

fileMEDIA said:


> I think both are very stable, but the handling for provider is easier by using kvm than xen. You can use any kernel and don


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## fileMEDIA (May 27, 2013)

AnthonySmith said:


> Sort of, you can use any kernel in Xen HVM, as it is hardware virtualisation, you are thinking of Xen PV, when RHEL 7 has native Xen support built in to the kernel no doubt ksplice will be fine.


I don


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## AnthonySmith (May 27, 2013)

Well I am going to do something very un-LET/B like and agree to disagree, this is the sort of conversation that could go on for 3 hours face to face, I understand your opinions I just don't share them 

edit: Your right Dom0/U wise with the kernels though, my mistake I obviously was not paying attention to what I was reading.


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## Marc M. (May 27, 2013)

*@**AnthonySmith* I would say KVM all day long, It's much easier to work with than Xen HVM and from my subjective observations it also seems to need less resources.


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## shahaz (May 27, 2013)

+1 for KVM


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## AnthonySmith (May 27, 2013)

Fair enough, my experiences are different but then I cannot honestly say I have benchmarked both on the same hardware, maybe I will do that


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## necs (Jun 6, 2013)

KVM is better for performance when it comes to windows.


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