Xen users - Jun 2009 - methods of porting RHEL PV guests to real hardware

As the subject states, I''m looking for pointers on porting
paravirtualized
RHEL guests from Xen back to real hardware.  It seems straight-forward
enough - ''yum install kernel'' to put a real kernel on the box.
Make sure
the menu.lst entries are ok.  Install the grub boot blocks on the hard
drive.  Etc. etc.

But how to get an initrd that closely matches the real hardware without *a
lot* of trial and error whilst manually specifying the kernel modules that
you think the real box will use?

-Ray


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----- "Ray Barnes" <tical.net@gmail.com> wrote:
> But how to get an initrd that closely matches the real hardware
> without *a lot* of trial and error whilst manually specifying the
> kernel modules that you think the real box will use?
> 
> -Ray
> 
Of course an easy, if not somewhat brute force way to do this is to install RHEL
on the target and then copy most of the filesystem over (bin, sbin, usr, opt,
var, etc, and lib <- but don''t whack the existing modules dir).

Usually all you need in an initrd is enough to get the root volume online and
the rest of the modules can be loaded from disk.  This should include the
storage controller and and device mapper features you are using like LVM. 
I''ve had to peel open a RHEL 5 initrd a couple times while setting up
boot from SAN + multipath, and there really wasn''t a lot in there.

I would start with scsi_mod, sd_mod, dm_mod, and then any specific hardware
module for your HBA.  For specific hardware, it may take some research to
identify the module name and all dependencies without having a system running
those modules.

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On Wed, Jun 24, 2009 at 8:42 AM, Thaddeus Hogan<thaddeus@thogan.com>
wrote:
>> ----- "Ray Barnes" <tical.net@gmail.com> wrote:
>
>> But how to get an initrd that closely matches the real hardware
>> without *a lot* of trial and error whilst manually specifying the
>> kernel modules that you think the real box will use?
>
> Of course an easy, if not somewhat brute force way to do this is to install
RHEL on the target and then copy most of the filesystem over (bin, sbin, usr,
opt, var, etc, and lib <- but don''t whack the existing modules dir).
Yup, that''s the most reliable method. I usually use LVM and have the
"original" root filesystem and the one from domU on separate LV.
> I would start with scsi_mod, sd_mod, dm_mod, and then any specific hardware
module for your HBA.  For specific hardware, it may take some research to
identify the module name and all dependencies without having a system running
those modules.
copying /etc/modprobe.conf from a real physical machine to domU, and
regenerate initrd should be able to handle most hardware drivers. LVM
is another thing though, so it''s easier to simply use a working initrd
(the previous method).

-- 
Fajar

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