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Microsoft Plans Hypervisor for Longhorn
ninjee writes "Microsoft reiterated plans to launch its own Windows-based 'hypervisor' software for running multiple operating systems. Bob Muglia, senior vice president in the Windows Server Division, said on Tuesday that the software will be 'built directly in Windows and will allow companies to virtualize multiple operating systems.' "
From TFA:
Microsoft's rival in this area is shaping up to be Xen [...] Xen doesn't yet support Windows, however
AFAIK Xen actually does support Windows, and it's not exactly a rival because it was originally sponsored by Microsoft Research - here is a relevant link
Having said this, I'm still convinced that full virtualization is the wrong approach and the separation technologies such as Linux VServer, FreeBSD jails or Solaris Containers will ultimately kill hypervizors.
First, it's not "Shut Do.."
Oh really?
Sigur RÃs: I didn't know that Heaven had a rock band.
VMWare creates a virtual machine for your OS to run in.
e rformance.html) describes this better than I could.
Advantage: provided it's simulation is good, everything that runs on the real hardware runs in the virtual machine
Disadvantage: that compatability comes at a significant runtime cost, which makes VMWare mainly used only for testing purposes, not for running multiple OSes for general work.
Hypervisors (like Xen) and what MS is claiming (I will believe this when we see it given the list of things they've dropped) use a technique called paravirtualisation to vastly reduce the speed problems. However, this requires support from the host OS. The Xen performance page (http://www.cl.cam.ac.uk/Research/SRG/netos/xen/p
Beware the psychokinetic mimes!
I'm attached to the Xen project, so I have an obvious bias ;-)
;-)
Nevertheless:
* I'd consider Xen a true hypervisor because it runs on the "bare metal" and multiplexes multiple "supervisor" kernels on top of itself.
* It was *not* designed as a full virtualising hypervisor, however.
* Paravirtualising gives better performance than full virtualisation on x86 - however full virtualisation is still nice for running things like Windows.
* Full virtualisation will be available on Intel Vanderpool / AMD Pacifica machines. Before those are ubiquitous, if you want to run virtualised Windows with maximal performance, yes, you should run VMWare
"vmware does not emulate the cpu"
This is not strictly true. It runs most of the instruction set natively, but emulates those portions of it that must run in supervisor mode.
Unfortunately this is complicated by the fact that some of the x86 instructions cannot be easily detected at runtime. This is one of the ways Xen simplifies things, by basically removing those tricky instructions from the instruction set and executing them only in the hypervisor.
I'm a Xen dude but I'll try not to be biased ;-)
:-)
Xen: paravirtualisation - modify the architecture dependent code of an OS so that it's hypervisor-aware
Pros:
* near-native performance
* simpler hypervisor
Cons:
* need to be able to port OSes (i.e. can't run Windows)
- NB this will be solved on Intel Vanderpool / AMD Pacifica CPUs
* need to run a non-standard kernel
- NB Xen support is integrated into the NetBSD mainline already and will be in the Linux mainline soon(ish). At that point, the Xen-aware kernel will be standard
VMWare (and MS Hypervisor, assuming it supports full virtualisation): full virtualisation - fake out an x86 machine in its entirety
Pros:
* Run Windows
* No kernel patching needed
Cons:
* Peformance penalty for kernel-intensive and IO intensive workloads
- NB VMWare mitigates this somewhat using custom VMWare-aware drivers to improve IO performance
- NB The MS Hypervisor provides these virtual drivers AND explicit APIs like Xen, so ported OSes can avoid these penalties
* Hypervisor is more complex
- NB nothing you can do about this if you want to support unmodified OSes on vanilla x86(_64)
The Xen and MS Hypervisors both have better hardware support than VMWare ESX because they run standard drivers in a virtual machine, rather than supporting them in the hypervisor itself. Note that VMWare GSX and Workstation don't have this problem because they run inside a host OS.
HTH,
Mark