Re: [Xen-devel] xen vs. vserver

[Mark Williamson <Mark.Williamson@xxxxxxxxxxxx>]

> In your faq and performance comparisons I don't see anything about the
> differences between xen & vserver. What is the difference. What will I
> get using xen?

I would expect the performance difference between vserver and native Linux to 
be virtually nil, so imagine all the Linux bars in the benchmarks were for 
vservers.  Xen offers a whole load of other features, over vservers:
* Stronger resource isolation between VMs (last I heard, some of this was 
available for vservers with additional patching but I think Xen's approach is 
more comprehensive)
  - VMs are scheduled pre-emptively
  - there are strict controls on VM memory usage
  - processes in one VM can't use all the file descriptors on the system and 
thus deny service to processes in another VM
  - etc, etc.
* Stronger security guarantees
  - kernel exploits in one virtual machine do not compromise the other virtual 
machines on the system
* Live migration of virtual machines
  - move running virtual machines to another host without stopping them
* Suspend / resume of virtual machines
  - pickle a virtual machine's state to disk and resume it later
* Run a different (user-specified, if you want) kernel in each virtual 
machine.  These may be different versions of the Linux kernel, or other OSs 
such as FreeBSD, NetBSD, Plan9.  This does not imply any extra trust of the 
user concerned.
* Give a single virtual machine multiple IP addresses on multiple virtual 
interfaces
* A couple of less commonly used features that we hope to expand upon are:
  - vnets (secure virtual link-layer networks that may involve multiple 
virtual machines on multiple hosts)
  - driver domains (sandboxed, restartable device drivers so that driver 
faults won't bring down the machine)

> I know several who are using vserver and have also tried it myself. I
> probably also try xen ;-)

Personally I really like both Xen and vservers.  I think they're complimentary 
technologies - it should be possible (with a bit of patching) to run vservers 
within a Xen virtual machine.

HTH,
Mark

> Please reply directly to me, i'm not the list
>
> Regards
> Hasse H. Johansen
>
>
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