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As there is a Cygwin which is API-level VM, I guess there maybe similar one in Linux?

Or, generally which hypervisor is fastest? I'm only care about Linux.

BTW, I can't install Xen in Ubuntu Maverick, so I can't have any experience on it.

BTW2. I'm searching for light weight hypervisors, to research distributed computing, distributed sessions and networking topics.

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Add that comment to your question. – Sasha Chedygov Nov 24 '10 at 7:59
Hypervisors are what VMs run on top of. – paradroid Nov 24 '10 at 19:39

kvm is pretty fast, but as with all things it depends on how you set it up. You'll likely find the I/O is the bottleneck.

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lxc Linux Containers are lower overhead than any solution which virtualizes the whole kernel. Like Linux VServer or OpenVZ, each "container" shares the same kernel with the rest of the system, but other resources (filesystems, users, network, process trees) are separated. While these three have varying capabilities, lxc has the distinct advantage of being integrated in the mainline kernel already – no third-party patches required, works on all hardware, etc.

I'm currently using LXC to virtualize various build environments (Debian, Ubuntu, Fedora) inside my Gentoo host system, and it works well.

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Cygwin is not really a VM. Its an API-level emulator.

Having used a number of VM products, the one I find fastest for everything I have thrown at it is VMware player. Its also free.

Xen and its various derivatives are reasonably good, I've just found on the same h/w that VMware seems to do better.

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Take a look at Linux VServer, which is a kernel-level "VM"; all your virtual machines will use the same kernel, but have different userspaces.

I haven't had time to play around with it a lot, but from what I've seen, it could be what you're looking for.

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ProxmoxVE uses a lightweight perl interface to KVM, with a smaller footprint than the libvirt library, that's a C variant AFAIK. It's a minimal bare-metal server-installation.

QEMU's pretty quick, especially if you remove the vCPU compatibility & let the guest have at the host CPU functions directly.

Recent improvements to paravirtualized drivers have allowed network throughput to jump approximately 8x what they were with previous offload methods.

QEMU also lets guests have a physical disk from the host as their virtual disk, removing the overhead involved in using disk images, although .raw images on LVM is still quite fast & provides the valuable snapshot functionality.

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I cannot notice any difference between running on bare-metal and running on VMs on VMware ESXi. It can run from a small USB flash drive, so I would say that it is pretty lightweight.

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Ever ran a true enterprise workload on VMware? – Xepoch Nov 24 '10 at 20:32
@Xepoch: I've worked with a law firm that runs DC and Exchange servers on VMware Infrastructure/ESX for 250 users. – paradroid Nov 24 '10 at 22:58
I've deployed countless instances of our classical software stack on various VMware instances (each >5k concurrent users). I have never seen them perform even close to bare metal or LPARs. It is fine software, just IMO far from being capable to support what is needed from IO spin locking. – Xepoch Nov 25 '10 at 3:10
I have a small site running VMWare ESXi (the free one) on a 4 core Xeon with 8 GB RAM. The machine runs 3 instances of XP, with plans to go to 4 or 5. You'd never know that they are not running in the bare metal. ALL hypervisors will have issues if you have extreme I/O needs, though. – quickly_now Nov 26 '10 at 4:36
@Xepoch: Why is the data not kept on SANs? I don't know how much virtualisation is used at that scale anyway, but my friend that works at the T-Mobile datacentres in the UK (with massive user numbers) says that they would never use it there. In any case, I still think VMware ESXi is well worth the OP considering for his use. – paradroid Nov 26 '10 at 8:55

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