Xen users - Jun 2009 - domU with 64-bit kernel, 32-bit userland - OK?

I''ve just started playing around with Xen and am probably going to P2V
some servers over to it pretty soon. One thing I just tested for the P2V was to
run a restore from a current backup into a filesystem on my Xen host. Then I
just made the fstab and getty tweaks and booted the domU with the kernel on the
host (vmlinuz-2.6.26-1-xen-amd64).

This sure made for an easier P2V than a re-build of the system and re-deployment
of the applications and configs. Only thing is, after I was playing around with
it for awhile I realized that the server I P2Ved was 32-bit.

Everything seems to be working fine running the 64-bit xen kernel and the 32-bit
userland.

The question is: It works, are there reasons I should not run it this way for
the time being?

Thanks! 


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On Mon, Jun 22, 2009 at 7:22 AM, Thaddeus Hogan<thaddeus@thogan.com>
wrote:
> Everything seems to be working fine running the 64-bit xen kernel and the
> 32-bit userland.
>
> The question is: It works, are there reasons I should not run it this way
> for the time being?
Are you using iptables, LVS, or someother program that requires
intensive interaction between userland program and kernel modules?  If
yes, you''d probably get some errors or warning trying to run it. If
you don''t, or whatever you use works fine, then you could stick with
your current setup.

Note that you have another option: using 32bit kernel for your domU,
located on domU''s fs, and load it with pygrub. You can run 32bit domU
kernel on 64bit hypervisor just fine. This way managing domU kernel
will be similar with physical servers or VMware guest: kernel
management is done from within domU.

-- 
Fajar

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On 6/21/2009 6:22 PM, Thaddeus Hogan wrote:
> I''ve just started playing around with Xen and am probably going to
P2V
> some servers over to it pretty soon.  One thing I just tested for the 
> P2V was to run a restore from a current backup into a filesystem on my 
> Xen host.  Then I just made the fstab and getty tweaks and booted the 
> domU with the kernel on the host (vmlinuz-2.6.26-1-xen-amd64).
>
> This sure made for an easier P2V than a re-build of the system and 
> re-deployment of the applications and configs.  Only thing is, after I 
> was playing around with it for awhile I realized that the server I 
> P2Ved was 32-bit.
>
> Everything seems to be working fine running the 64-bit xen kernel and 
> the 32-bit userland.
>
> The question is: It works, are there reasons I should not run it this 
> way for the time being?
I have been using a setup for months that includes several 32 bit PV 
machines using the 64 bit kernel from the host. They haven''t had any 
problems. Except for applications but these are using for software 
testing so that is expected. Things have worked great in that situation 
for me. I have been using Debian Etch and Lenny as the hosts and vms.

mike


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