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Xen .vs. KVM

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Mad Penguin:
For anyone looking at getting into virtualisation and wondering about these two technologies, here's a brief run-down of the differences between the two which should hopefully give you an idea of where to aim.
Xen KVM1.Runs on pretty much any hardware Needs a CPU with hardware virtualisation support, probably something manufactured within the last three years2.Tied to a specific kernel, in particular you will be limited to 2.6.18 or 2.6.22 Runs on the stock Linux kernel, built into and supported by Ubuntu 9.10 for example3.Been around for a while, lots of support available, all the gotcha's have been found and there are fixes for many of them Is much newer and still under pretty active development, new gotcha's appearing together with new fixes. This is a far more 'dynamic' environment4.Typically wants to run on a dedicated server, not a good desktop platform Is happy to run as a desktop platform with VM's in the background5.Only supports 'windows' when your CPU has virtualisation features and needs a different config style Only runs at all if your CPU has virtualisation features, but then treats Linux/Windows equally 6.Typically needs to be configured by hand Typically supplied with and configured by GUI7.Marginally faster in terms of performance / overhead, but not much in it Faster in terms if IO and attached device drivers8.Poor / buggy support for new kernel features and filesystems Current kernels == as good as is available on non-virtualised systems9.Is happy to tune memory usage and attached devices on a running system These features are under development and work in certain circumstances, but changing the memory on a running instance is for example far more 'hit and miss'10.Handles SMP pretty well Instances with n-way SMP configured have a nasty habit of running slower than single core / non-SMP instances11.Has some nice tools for system monitoring (xentop for example) Is limited to 'libvirt' and not so good, also subject to excessive system 'load' for no apparent reason (this is a current 'bug')
Any other thoughts welcome .. I'll try to update this table with any important points once someone points out I've missed them off ...  :)

If there are any VMWARE users out there who also use KVM or XEN, a KVM .vs. VMWARE or XEN .vs. VMWARE would be quite interesting ... ??

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