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Re: [Xen-users] 64bit 32bit question

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Subject: Re: [Xen-users] 64bit 32bit question
From: Mark Williamson <mark.williamson@xxxxxxxxxxxx>
Date: Sun, 9 Dec 2007 00:04:05 +0000
Cc: Jens Ahrens <jensampol@xxxxxxxx>
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> I have to install several virtual machines on a server
> with 2 x XeonQuad and 32GByte RAM. The Problem
> is that I have to run 32bit software on the virtual
> machines.
> What can I do?
> 1) Install a 64bit Linux on the server to be able to
> use the 32GByte RAM
> --> Problem: Can't set up 32bit xen kernel for the
> virtual machine on 64bit Server

Since Xen 3.1 you can run 32-bit dom0 and domUs on a 64-bit Xen.  There are 
some restrictions (suspend / resume and migration may not work) but the 
domains will run OK otherwise.  At least some of these restrictions will 
probably be relieved in 3.2.

> -----> Solution: Use HVM but this costs too much
> performance

Have you tried it?  It may perform OK, depending on what you want to do.  
There's also a halfway option here in that you could install PV drivers in an 
HVM domU.  That also would require the 32-on-64 support available in 3.1.

> -----> Solution: Use 64bit xen kernel and install
> 32bit rpms?

You could do that, but a true 32-bit kernel would perform even better and be 
a "genuine" install.

> 2) Install a 32bit Linux on the server
> -->Problem: Can I access the full 32GByte for the
> domUs?

I think the answer to this is "yes", but you wouldn't be able to run 64-bit 
domUs...  Even if you had a 32-bit dom0 you could still install a 64-bit Xen 
later on and gain the ability in run 64-bit domUs, though, so you shouldn't 
get "locked in".


Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

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