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19 Comments
- jdong, on 10/12/2007, -0/+11Xen is paravirtualization through a hypervisor. Think of Xen as an OS for an OS. Xen runs OS'es as processes -- so even your 'host/primary' machine is running under the Xen hypervisor.
KVM is more like traditional virtualization that there is a more distinct 'parent' and the parent runs virtual machines.
Xen does not necessarily need virtualization extensions while KVM does.
Xen affects kernel-driver compatibility. i.e. a driver that works natively on the host may not work under Xen (somewhat true for fglrx/nvidia drivers though patches are available for them to run under Xen). KVM does not affect the host in that way. - sishgupta, on 10/12/2007, -1/+10Is KVM even trademarked? I just thought that was what the generic device was called.
- bigtomrodney, on 10/12/2007, -1/+6But isn't KVM already in the kernel? They'll have to choose not to include it rather than not choose to add it in.
- inactive, on 10/12/2007, -0/+5KVM is a kernel module you can load in to your current Linux kernel (e.g., linux-2.6.20)
Xen is its own separate kernel (e.g., xen-2.6.20)
I prefer KVM, since I can rmmod the kernel module whenever I want. Plus, the 3D Nvidia drivers don't work with Xen yet. Damn you NVidia!
EDIT: Beaten by jdong, but he went into more detail - shuffle2, on 10/12/2007, -0/+4can someone explain the differences between xen and kvm?
- inactive, on 10/12/2007, -4/+8KVM and Xen are both in the Ubuntu Feisty repos.
- naxx, on 10/12/2007, -1/+5KVM will only make it into Fedora 7 but not into RHEL, because of a deal with Xen, I think, for the next 5 years. And of course, KVM is not mature enough yet.
- newmind, on 10/12/2007, -0/+2I agree. Why couldn't someone have used some common sense and called it KV (Kernal Virtualization) or KVE (Kernal Virtualization Engine) so as not to compete with an already ubiquitous acronym. I'm sure the people that came up with this are infinitely smarter then me but that acronym is stupid.
- jdong, on 10/12/2007, -0/+2"In the [vanilla] kernel [sources]" does not mean that Fedora's kernel configuration will activate the functionality or provide the userland utilities to support it.
- dtfinch, on 10/12/2007, -2/+3Terrible choice of acronym.
- Scruffydan, on 10/12/2007, -1/+2just so everyone knows i wasn't being serious, i just found it funny that the virtualization people could find an unused acronym.
... that is all - jimmytango829, on 10/12/2007, -0/+1One big difference that no one mentioned yet is that under Xen you can dynamically re-allocate resources (like ram and disk space) to the virtual machines, and under KVM you cannot. I'm not entirely certain, but I don't believe KVM has the ability to move a running virtualized environment to another machine either (Xen can).
Both of these features are quite nice for clusters of virtualized servers. - centauri, on 10/12/2007, -0/+1It has something to do with the way they virtualize things. This is what i found on Google - http://www.gridvm.org/xen-vs-kvm.html
- jdong, on 10/12/2007, -0/+1Migration is planned for KVM but you are correct -- right now Xen fills the niche for like a massive virtual server farm while KVM appeals more to Joe User wanting to set up a few testing VM's for the latest Linux distros and whatnot :)
- fleabag, on 10/12/2007, -0/+1libvirt ftw.
- aetherane, on 10/12/2007, -0/+1KVM is essentially a kernel driver that schedules the virtual machines as processes. It can be started and stopped while the machine is running and has no real affect on the system when it isn´t running - there is little ¨cost¨ to including it in the kernel source tree.
Xen is an external hypervisor that sits below the kernel. The kernel modifications are not to add Xen to the kernel but to make the kernel run on Xen (using paravirtualization).
KVM is starting to have support for paravirtualization, which means that kernel modifications may be used in the future (but probably only on guest Kernels). - ceplm, on 10/10/2007, -0/+0RHEL 5 has (and always will have) only 2:6.18 which doesn't have KVM.
- wolfzero, on 10/12/2007, -7/+2Kernel Virtual Machine Virtualization...isn't that a bit redundant? Plus, not explaining you're not talking about what 99% of dig users will recognize as 'keyboard/video/mouse' is just plain dumb. Oh and why do I care about this? No digg.
- Scruffydan, on 10/12/2007, -14/+1KVM = keyboard video mouse
I smell a trademark dispute... but only a small one... that no one will notice
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