Re: [tlug] xen and windows

["Stephen J. Turnbull" <stephenjturnbull@example.com>]

>>>>> Darren writes:

> So, what's all this about Xen and windows? I've read up enough to know I
> need an Intel "VT" CPU. But does it just work?

Supposedly AMD had a feature equivalent to VT ("virtualization
technology"?); does that not work?
I've been really happy with the performance on my Opteron boxes,
though the price may be higher than you want to go, I don't know.

As for "just work", yes and no.  The theory of VT is that a monitor
like Xen can just do very low level stuff like granting access to
hardware and process switching (each OS is the equivalent to a
process) without help from the guest OS.  This just works, although
there are probably still bugs in the VT implementation.  But you
shouldn't have a problem with that.  (VM, on the other hand, depends
on substantial help from the guest OS.)

What isn't going to "just work" is that you still have shared
resources to manage, and this is non-trivial.  (Consider that the
smartest, most flexible, shared resources available are *people*, and
that matrix management is now a fad of the distant past.)  I think I
posted just about a year ago about my experience with PVM which is the
process equivalent of a virtual machine monitor: due to communication
contention, a multiprocess parallel program ran 2 orders of magnitude
slower than a one-process version of the same.

So, maybe you'll get lucky.  Everything you want to do "just works",
and does so efficiently.  This is IMO the most likely case, at least
for your basic applications.  And maybe you won't, in which case
you've increased the odds of running into a fiendishly difficult
debugging problem.

> Can I buy a new machine
> with windows pre-installed, then add xen and linux afterwards?

I think you can do this, but you *will* have to resize Windows
partitions.  I've never had much success with that.

> Or does xen and linux need to go on first?

I recommend that you have an install disk for Windows, not one of
those awful "Windows in a hidden partition" deals.  Up to XP, a
reinstall has always been the remedy of choice for a horked Windows
installation, and I can't imagine that Vista is any different.

> P.S. xensource.com is running aspx pages: is that a good or bad sign? :-)

It says either that they don't care about security, or that they have
enough money that they can afford a full time person to monitor the
intrusion monitors and make sure that all patches are applied and
things nonetheless go smoothly.  The former is a bad sign, the latter
is a good one.
:-)

And, of course, get lots of memory.  At least 1GB for each guest OS,
and at least 2.5GB per Vista instance (that includes the 1GB for Vista
as a guest OS).

I have to wonder if you wouldn't be better off using Mac OS X and
Parallels, though.