> -----Original Message-----
> From: Tomasz Chmielewski [mailto:mangoo@xxxxxxxx]
> Sent: 24 January 2007 16:36
> To: Petersson, Mats; xen-users@xxxxxxxxxxxxxxxxxxx
> Subject: Re: [Xen-users] migrating 32 bit guests between 64
> and 32 bit hosts - possible?
>
> Petersson, Mats wrote:
> >> -----Original Message-----
> >> From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx
> >> [mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of
> >> Tomasz Chmielewski
> >> Sent: 24 January 2007 16:01
> >> To: xen-users@xxxxxxxxxxxxxxxxxxx
> >> Subject: [Xen-users] migrating 32 bit guests between 64 and
> >> 32 bit hosts - possible?
> >>
> >> Is it possible to migrate a 32 bit guest from a 32 bit Xen
> >> host to a 64
> >> bit Xen host?
> >>
> >> As I understand correctly, it's only possible when one
> runs a 32 bit
> >> dom0 kernel on a 64 bit CPU?
> >
> > At the moment, migration (in the Xen sense) is only supported by
> > Para-virtual, which in turn means that you'll need to have
> both Dom0 and
> > DomU kernel being the same size as the hypervisor.
> >
> > So the most likely scenarion to solve this would be to use a 64-bit
> > kernel instead of the 32-bit kernel with the rest of the
> distro either
> > 32- or 64-bit.
>
> But if I use a 64-bit guest kernel, I won't move it to a 32-bit host.
>
> In other words:
>
> it's not possible to migrate (or even start), para-virtual:
>
> a 32-bit guest kernel on a 64-bit kernel Xen-host?
No, the guest kernel (both DomU and Dom0) has to be "the same size",
i.e. 32, 32PAE or 64. Combining different sizes will not work (Dom0 will
not boot, and domain-builder will complain about the guest kernel).
So you need to decide if all your hosts are 32-bit or 64-bit. If you
have some hosts that can't run 64-bit, then you'll have to use 32-bit.
If you have large memory on some machines, you may want to consider PAE,
as that will give you 32-bit kernel, but also ability to access above
4GB of RAM, so you get (sort of) the best of both worlds (except that
your apps still only get about 3GB per app to work within, rather than
the "almost infinite" limit that the 64-bit address space allows for).
There is work to allow 32-bit PAE on top of 64-bit guest, but I don't
think it's quite ready for production yet - although that's not
something I work on, so I could be wrong.
--
Mats
>
>
>
> --
> Tomasz Chmielewski
> http://wpkg.org
>
>
>
>
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