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Re: [Xen-users] 32/64 bit confusion

To: Joe Auty <joe@xxxxxxxxxxxxxxx>
Subject: Re: [Xen-users] 32/64 bit confusion
From: Rudi Ahlers <Rudi@xxxxxxxxxxx>
Date: Wed, 02 Jul 2008 08:42:52 +0200
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Joe Auty wrote:

I just discovered that the 32 bit FreeBSD works fine for me as a guest OS, but the 64 bit version doesn't. My host is a 64 bit Intel machine that supports full virt.

Does Xen support 64 bit guests? Is there any benefit to running a 64 bit guest on 64 bit hardware performance-wise, or are there bottlenecks (e.g. Xen itself not being 64 bit).

I'm debating whether KVM + 64 bit FreeBSD vs. Xen + 32 bit FreeBSD would ultimately be faster for me, or whether the difference would be negligible? I know that 64 bit does not equal faster, and my machine also doesn't have more than 4 gig of RAM, so perhaps I'm splitting hairs...

Anyone care to straighten me out? :)

Sure Xen can run 64bit guests, as long as the dom0 host OS is 64bit as well. We run CentOS x64 + Windows 2003 x64 & CentOS x64 guests. I still have to try and install FreeBSD, but that's for another day.

64bit has more benefits than just being able to address the extra RAM. 64bit PCI cards also has more pipelines, so there will defanately be a performance increase there as well

By the way, you don't need 64bit to address 4GB RAM. The Pae kernel can address up to 16GB on 32bit machines.


Kind Regards
Rudi Ahlers
CEO, SoftDux

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