Xen Hacker Interviewed

Drawoc Suomynona writes "The Xen virtual monitor is a new generation virtualization software that enable running multiple OSes at the same time with unprecedented level of performances. Manuel Bouyer was recently interviewed about his work porting Xen to the NetBSD operating system. The interview touches on why some consider Xen to be so good, how hard it is to integrate such a software package into an OS, and more."

Re:OS X ?

[simcop2387]

no, Xen requires changes be made to the kernel of the guest operating system, this can't be done with Windows, it could possibly be done with OSX though

Xen on Windows

[Aladrin]

I see a ton of comments about not being able to use Xen to run Windows inside Linux, but no information the other way around...

Can Xen run Linux apps on my Windows installation? I am currently using Cygwin for that, and it's working okay, but some of my favorite apps are being run through SSH from my linux box to make all this happen.

I do too much in Windows to even dual-boot the system... I'd spend as much time booting as I would working/playing.

Migration

[Stoned4Life]

"Xen also offers virtual machine migration, where you freeze a Xen guest, move it to another machine and resume it there ... This also means that a similar environment for the guest has to exist on the remote system."

And if a similar environment is not available when it is moved, what happens to the state of the user? Would the hardware in use when the state is saved have to be exactly alike on the target machine?

Also, is the information retained on the backup until the full migration is completed and then deleted, or is deleting the backup during the migration optional, leaving a "frozen" and "restorable" state on the server? Is that a security risk if the workstation is compromised?

Now THIS is cool

[ScrewMaster]

Xen virtual machines can be "live migrated" between physical hosts without stopping them. During this procedure, the memory of the virtual machine is iteratively copied to the destination without stopping its execution. A very brief stoppage of around 60-300 ms is required to perform final synchronisation before the virtual machine begins executing at its final destination, providing an illusion of seamless migration. Similar technology is used to suspend running virtual machines to disk and switch to another virtual machine, and resume the first virtual machine at a later date.

(Quote from Wikipedia)

Reminds of when I was watching the old Max Headroom show, and Max would shuffle himself off of one monitor onto a display on a portable "processing unit" and somebody would pick him up and carry him away.

Re:What I want from virtualization

[Anthony Liguori]

What I want from OS virtualization is to be able to run one guest OS on multiple hosts for redundency.

Then what you want is Marathon [marathontechnologies.com] style lock-style execution. It's a terribly hard problem because you have to make all software run deterministically (timers and IO events on both machines have to occur in the *exact* same moments in execution).

Regards,

Anthony Liguori

Try VMWare ESX Server 3

[supachupa]

VMWare ESX Server 3 (currently in beta) will probably get as close as you can to having live fault tolarant servers. By sharing a storage such as SAN or iSCSI, it is able to instantly take over when it detects the failure of another physical box and should not lose any sessions or data. The other cool thing is that it can dynamically move a running virtual machine to a less loaded physical server. Still, it is not running two virtual machines simultaneously like you've described.

Re:VMWare Player...

[thehunger]

You're right. Any you'll be glad to know that VMware has decided to provide a updated and FREE version of its GSX Server. This will allow you to CREATE virtual machines as well as run several VMs timultaneously. Also it can do SMP and 64-bit emulation, so you'll be able to install a 64-bit multi-processor version of an OS on your current 32-bit single processor computer...

  It's called VMware Server and is in beta now.

However, it's not -entirely- free: VMware will charge for support, and there's no guarantee that updates and patches will be available for non-paying customers.

Re:Migration

[kscguru]

Xen doesn't do graphics cards (at this point, everyone - even VMware - virtualizes graphics cards). Network cards, you only get via a virtualized Xen network adapter with Xen drivers, so those will remain the same. Nobody does passthrough hardware - nobody.

You will find processor differences though. Move from AMD to Intel, or drop SSE extensions or some such, and things will break.

Re:Xen on Windows

[TallMatthew]

The reason they call it a hypervisor is just that, its a step above a supervisory process. On VT enabled platforms (The new P4's / AMD's) you really start to see what xen can do without the bottlenecks of processor architecture.

I would think your bottlenecks would be constant context switches on your proc, cache misses on your virtual memory and seeks within your RAID (at the "hypervisor" level). No matter how good your top-level kernel delegates, it's still a level of indirection before control is passed to the kernels within your virtual machines (who obviously do their own prioritization). If you're running a cluster within a box, this constant delegating and shuffling of data from disparate elements to disparate kernels with disparate priorities would require constant and massive data shifts within the host machine and bring said box to a crawl, wouldn't it?