Re: [Xen-users] 32bit or 64bit dom0?

["iS-Fun Internet Services GmbH, Holger Diehm" <h.diehm@xxxxxxxxx>]

Hello,

your question is just right for me to tell about my experiences of the last 
two weeks, when I migrated some older xen Dom0 installs to newer xen 
versions.
I can only talk about pv, because thats the only thing we need (atm).
First I set up two new 64bit Dom0 Debian servers. Compilation of xen 3.4.2 
from source worked fine.ocumentation set aside - I don't need it.
I directly booted into an 2.6.31.12 xenified kernel - 64 bit - this kernel so 
far works like a charm - search the list for the patches for 2.6.31.

The 2.6.18.8 Kernel from the xen-mercurial tree was built for some legacy 
DomU-32bit-Systems, which threw me libsysfs Errors on boot (some earlier 
SuSes) - works as expected too :-)

These legacy Systems were on a xen 2.0.x and have to run on for some more 
time, the "newer"  were migrated from xen 3.0.x.

As you can see, just any paravirtualized DomU - 32 or 64 bit run on that 64bit 
xen-Dom0 just fine.
I booted in various GNU/Linux system-flavours just swapping my xenified kernel 
with the distribution-kernel - centos,SuSe,debian,gentoo.
The interesting point is, that a recent 32bit DomU even runs with the 
64bit-Kernel - but very soon I decided to build an extra 32bit DomU-kernel, 
just to not confuse any tool that depends on the arch reported by the 
kernel - build tools etc can be easily confused by a wrong "uname".

So I have three different kernels - 2.6.31.12Dom[0U]64bit, 2.6.31.12DomU 32 
bit an 2.6.18.8DomU 32 bit - all 32bit Kernels are PAE-enabled.
I ran several tests and there is just nothing ugly to report :-)
32 bit VMs run alongside 64 bit VMs, no Problems.

The basics are reported everywhere - old xens allowed to have the tty1 as 
console . Rename all tty1 to xvc0... see inittab, securetty, and settings for 
console in the DomU configuration, if you haven't already.
Perhaps create the device under /dev - if not available.
If you use filebased Images, switch from file: to tap:aio: in your DomU config 
file. It works well and you don't run into any loop-device issues.

What I often thought is a mistake, was my helping-hand with those 
old "unportable" DomUs...the "ancient" but still maintained 2.6.18.8 kernel 
from xen-mercurial.
None of them ole DomUs ran with a recent kernel !
That is perhaps one thing you should *really* take into account for your 
Upgrade - test the DomUs with the newer Kernels you plan to use, and if you 
run into troubles, look for a matching xenified-kernel.
This made it a nice job for me to migrate old xen DomUs to newer versions.

So I couldn't tell you the route to take, but perhaps some of the 
above "signs" help yout to take your route "your way".

So thanks to all the guys who feel responsible to push xen forward..not only 
to newer kernels :-) And to all the unnamed contributors.

Cheers,

Holger

Am Monday 25 January 2010 21:08:06 schrieb Ian Tobin:
> Hi,
>
>
>
> Just wondering what the best route to take is.  We have been running
> 32bit Dom0s for the past few years but we are refreshing all our
> hardware and the question is to which route we take.
>
>
>
> I assume we can run 32bit domUs ok on 64bit dom0?
>
>
>
> What is everyone else doing? Any issues?
>
>
>
> Thanks
>
>
>
> Ian



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