Web Hosting Talk : Web Hosting Main Forums : VPS Hosting : virtualisation qemu

[warg]

Does someone has experience with the virtualisation 'qemu'? What are the advantages/disadvantages of it compared to Openvz.

Thanks for reply

[rds100]

qemu is the same as KVM. It is real virtualisation (with virtual hardware) so it can run things like windows, freebsd, etc. But since it is real virtualisation there is also more overhead compared to OpenVZ, so worse performance (on the same underlying hardware).

[rimote]

I agree completely with the answer, exept thath quemu it is not the same as KVM. Instead KVM usually uses it to emulate the hardware. Of course just emulating hardware (quemu is particulary good at rendering differnt CPU types) is not the whole deal. KVM has to do a lot more like memory-sharing and so on. These two things make it like rds100 said quite a lot slower than OpenVZ.

[Boris A Dolgov]

I would say that not KVM uses QEMU to emulate hardware, but QEMU can use KVM to emulate processor and memory.
So, if you use KVM, you almost have no overhead for CPU and memory, but have overhead on network and disc IO, that are still emulated in QEMU. Virtio (which is supported by most Linux distributions and even Windows) can make this overhead very low.

Comparing to OpenVZ, QEMU+KVM gives you a lot of benefits: you can use custom kernel and non-Linux OSes, VPSes are better isolated.

QEMU without KVM is almost unusable for VPS hosting, because it slows down machine CPU nearly 50-200 times.