[Fedora-xen] Guests from other distros

[John Summerfield]

John Summerfield wrote:
> Tom Horsley wrote:
>

>> http://home.att.net/~Tom.Horsley/xen-fci.html
> 
> Thanks Tom.

I'm well into reading it. Good, humorous.

Some comments:

I have had a short play with Microsoft's Virtual PC. Only a short play
is necessary to run Linux (I booted an INSERT CD and it ran find), and
to install Windows 2003 Server. In the traditional MS way, one starts a
wizard, answers a few questions and it's done. Starting it involves
running a standard-looking BIOS which one can configure (choose boot
device and so on, not a lot in there).

It's simple and fairly sensible. I don't recall what hardware it
emulates, BX chipset I think, and definitely Dec Tulip network card.

Almost certainly will run OS/2, which I saw mentioned in the Wizard.

What's a pygrub?
This is FC/Red Hat. Jeremey K wrote it. I wish he'd done something a
little different. I don't think it's likely to boot from (emulated)
Floppy, CD or Network.

SUSE has a script to get the kernel out of an image. I don't think it's
as good.

Ubuntu (and Debian) appears only to support an external kernel., but I
might have missed something. An external kernel is good if you want to
use a xen kernel to run something such as Sarge or RHEL 4 without the
hardware support.


============
(but I wonder if it would let me change CDs if I had to install from CD
- stay tuned to this thread for more info)

I think it was in SUSE (maybe even SLES10) documentation I read this
"does not work but we're working on it." But it might have been RHEL5. A
DVD is fine - no swapping.


============
I get the impression that memory usage can't be dynamic,

I've managed to reduce Dom0's RAM on the fly, on a test machine I didn't
have enough until I did.

Logically, hot-plugging RAM (and CPU) should work, it's supported by
some hardware.

Oh, I did expand a guest's RAM too. The guest (running Anaconda at the
time) didn't notice.

=============
Another important fact to note is that you can't have the same disk
partitions mounted at the same time in multiple guests or in guest and host

You can. Read Only everywhere. As soon as anyone writes to it, all
guests start crashing and burning.


==============
you just share the same swap partition
I don't like swap partitions. I like no swap (best) and swap files. One
can add swap files at any time, as dictated by need.


==============
Xen under Xen
(Not in Tom's document exactly like that, but touched on).
I read somewhere it's not supported.


Note. IBM has been doing this stuff for about four decades. IBM'
flagship implementation is VM and it runs on IBM mainframe. One brave
soul ran 42000 penguins at one on one mainframe.

IBM supports VM under VM, nested more-or-less indefinitely, but
performance falls off at the third layer. It has some hardware (or
firmware) support for some functions.







-- 

Cheers
John

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