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Re: [Xen-users] 32bit or 64bit?


  • From: "Peter Braun" <xenware@xxxxxxxxx>
  • Date: Mon, 6 Nov 2006 14:33:55 +0100
  • Cc: xen-users@xxxxxxxxxxxxxxxxxxx
  • Delivery-date: Mon, 06 Nov 2006 06:25:07 -0800
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  • List-id: Xen user discussion <xen-users.lists.xensource.com>

> Can I install the 64Bit Version of Debian for all domains
> inclusive dom0 and
> will windows run on it (do I need 64bit Version?). What about
> the stability?

You can run 32-bit HVM DomU on any equal or better Dom0, only
Paravirtual DomU needs to be "equal" (work is in progress to support
32-bit PV DomU on 64-bit).

However am using dom0 64-bit and 32-bit paravirtualized domU (debian) over 64-bit domu kernel.

 

>
> Or its better to stick with 32bit? PAE or non-PAE Version?

Either will work. With 4GB of memory, and if your platform supports
"Memory hoisting" (where the memory below 4G is moved to above 4G so
that the memory-space covered by PCI devices can be used elsewhere),
then you'd be better off using either 64-bit or 32-bit PAE so that the
memory above 4GB becomes available rather than lost. There may be BIOS
settings that enable this, or it may be "automagic", you'll want to look
at the initial E820 map from Xen to see how much memory is above 4GB (a
1 and 8 zeros is 4GB in hex). RAM is marked as "usable" in the E820 map,
and it's one of the first few things printed in the "xm dmesg" log (or
in the "dmesg" in your standard Linux kernel, but don't use Dom0's E820
to determine ACTUAL memory, as it gets modified by Xen to reflect what
Xen thinks Dom0 should and shouldn't see!).

I think it would be better for you to use 64bit dom0 because of much better memory handling.
Especially 4GB and more memory is always little bit problematic on 32bit platform.

You should use 32bit dom0 when do you plan to use for example netBSD of FreeBSD as paravirtualized domU which are
currently supported only under i386 platform.

Simply you cannot run 32bit kernel for paravritualized domU on 64-bit dom0.

So my proposal for you is to use 64bit dom0, HVM for Windows (can be both 32 or 64bit) and 64bit domu kernel to use for creating 32bit paravirtualized debian guests.

BR

Peter Braun
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