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This table compares the features and performance of the various virtualization technologies available for Linux. Hopefully this table also explains why many Linux distributions today ship Xen, even though UML and KVM are upstream and lhype is getting pretty close to inclusion into the upstream kernel.

For an explanation of the technologies, please see the [:TechOverview:technology overview] page.

If you spot something that is not up to date, or think of something missing, feel free to update this page.

full virt paravirt license x86 x86-64 IA64 PPC s390 performance SMP guests notes
Xen (./) (./) GPL (./) (./) (./) (./) paravirt very fast, full virt slow/medium (./) full virt needs VT / AMD-V
KVM (./) GPL (./) (./) still slow requires VT / AMD-V, upstream
lhype (./) GPL (./) slow/medium
rhype (./) (?) (./) (./) (./) fast (?) research project
MoL (./) GPL (./) fast 32 bit only
UML (./) GPL (./) (./) ?? (./) slow upstream
qemu (./) GPL (./) (./) ?? (./) slow/medium runs in userspace, kQEMU not GPL
OpenVZ GPL (./) (./) (./) (./) very fast shared kernel
VServer GPL (./) (./) (./) (./) very fast shared kernel, no performance isolation
VMware (./) proprietary (./) (./) medium (./)
LPAR (./) proprietary (./) native (./)
z/VM (./) (./) proprietary (./) very fast (./) typically runs under LPAR
PHYP (./) proprietary (./) fast (./) used on all modern IBM System p
lv1 (./) proprietary (./) fast (./) used on Sony PS3
BEAT (./) proprietary (./) fast (?) used on Toshiba CellEB

Notes:

  1. Paravirtualization is fundamentally faster than full virtualization, with the exception of the userspace implementation in UML.
  2. For an overview of the other benefits of paravirtualization, see ParavirtBenefits.
  3. Full virtualization performance in KVM and Xen is largely limited by the overhead of trap & emulate. Emulating multiple instructions at once at the time of a trap should bring it up to speed with VMware.
  4. OpenVZ (Virtuozo) and VServer are not virtualization technologies per se. They carve up a single system in "super chroot" jails. All the containers run on top of the same kernel.
  5. Qemu can emulate different guest architectures, eg. running an x86 virtual machine on a PPC guest. Qemu also has the distinction of being the only full virtualization technology that can run without root privileges.
  6. Parts of Qemu are used in the full virtualization implementations of Xen and KVM.