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Re: Xen, Squeeze, and Beyond

On Thu, Feb 25, 2010 at 04:53:56PM -0600, John Goerzen wrote:
> Hi folks,
> There was a thread here a little while back about the status of Xen in
> future Debian releases.  It left me rather confused, and I'm hoping to
> find some answers (which I will then happily document in the wiki).
> According to http://wiki.debian.org/SystemVirtualization :
> "Qemu and KVM - Mostly used on Desktops/Laptops"
Yes - but also the only game in town for cross platform emulation.

KVM is shaping up well and appears to be very well supported by Red Hat.

> "VirtualBox - Mostly used on Desktops/Laptops"

Who knows what will happen to this now that Oracle own it? It's possible 
it will be merged in one of their other products like Virtual Iron.

> "Xen - Provides para-virtualization and full-virtualization. Mostly used
> on servers. Will be abandoned after squeeze."

I think that the problem here is that Xen isn't mainstream in the 
kernel. It takes a long time for a Xen-ified kernel to come out and any 
distribution supporting it has to carry a heavy patch burden. Xen 
doesn't keep anywhere current in terms of kernel - if we release Squeeze 
this year with kernel 2.6.3*, Debian will have to maintain all the patches
/ "forward port" them to 2.6.32 or 2.6.33 as was done with 2.6.2*. 

Red Hat will support Xen for Red Hat Enterprise Linux 5.x, for example, 
primarily because it was there for 5.0 on 2.6.18. Red Hat now have a 7 
year commitment to a support lifecycle based on one kernel
release. The Red Hat kernel is already heavily patched (and takes 
18 months or so to release - by the time they stop supporting 5.x, 
the code will be almost 9 years old) - and the back patching of 
security fixes and requested features through the support lifecycle is 
a nightmare for them. I'd be slightly surprised if they commit to Xen 
through the lifecycle of their version 6.x.

> The Xen page on the wiki makes no mention of this.
> So, I am wondering about our direction in this way:
> 1) Will a squeeze system be able to run the Xen hypervisor?  A Xen dom0?
> 2) Will a squeeze system be able to be installed as a Xen domU with a
> lenny dom0?  What about squeeze+1?
> 3) What will be our preferred Linux server virtualization option after
> squeeze?  Are we confident enough in the stability and performance of
> KVM to call it such?  (Last I checked, its paravirt support was of
> rather iffy stability and performance, but I could be off.)
> 3a) What about Linux virtualization on servers that lack hardware
> virtualization support, which Xen supports but KVM doesn't?

Which servers that lack hardware virtualisation support - 
pretty much everything made in the last two or three years has it. For servers,
specifically, the likelihood is that - Lenny has a 2 year life + 1 year, 
Squeeze has ? year life + 1 year - by the time you get to Squeeze + 1 
anything that doesn't will be almost ten years old. QEMU will work. 
Non-Intel - ARM, PPC ... may be another matter.

> 4) What will be our preferred server virtualization option for non-Linux
> guests after squeeze?  Still KVM?
> 5) Do we recommend that new installations of lenny or of squeeze avoid
> Xen for ease of upgrading to squeeze+1?  If so, what should they use?

New Squeeze - use KVM? New Lenny - whatever you want, because at this 
point you have (days until release of Squeeze + 1 year) to find an 

> 6) Are we communicating this to Debian users in some way?  What can I do
> to help with this point?
> Thanks,
> -- John

Just my 0.02c

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