Re: [Xen-users] DomU in it's own LVM partition fails to boot CentOS 5.2 Dom0/U

["Fajar A. Nugraha" <fajar@xxxxxxxxx>]

On Sun, Jan 25, 2009 at 1:19 AM, Peter Hoose <phoose@xxxxxxxxx> wrote:
> I'm trying to do what I think would be relatively simple but can't seem to
> make it work. Essentially I want to create several domU's running CentOS
> each with it's own LVM partition for increased performance over image files.
>
Some would argue that with current implementation (i.e. with tap:aio
instead of files) and by using full (i.e. not sparse) image files you
can get a similar performance from file-based vbd compared to
LVM-based.

>From your post, I'd say you're trying to do two things at once :
- move from file-based to LVM-based vbd
- using whole domU disk directly as filesystem, without additional
partition/LVM on domU side.

When trying new things sometimes it's better to do it one at a time.

> Initially I did a test with image files and everything went fine, I booted
> the supplied initrd and vmlinuz images installed CentOS from http, etc...

That's good.

> However, the performance of image files is pretty slow for what I intend to
> use this for (Web/DB servers).

I'd recommend you try that one more time, but by making sure that :
- the generated domU config file uses tap:aio: instead of file: (I
haven't tested virt-install in a long time, so I'm not sure which one
it uses by default)
- use non-sparse image file

> So I wanted to do the same thing but in a
> dedicated partition. Problem is, when I do this and try to install via http,
> the disk doesn't show up in the installer, it just shows a "#". This appears
> to be expected when using a dedicated partition

No it's not. Any backend vbd on dom0 side should look the same to domU
when it's presented as the same device (i.e. xvda). However, changing
xvda to xvda1 has the effect that you mentioned.

> and the solution seems to be
> to copy an image to my partition and go that route. I tried this 2 different
> ways: 1: jailtime image 2: copy of my dom0 OS.

Actually there's door #3 :
- install to a file-based vbd (you got this already)
- copy files (or copy the whole domU disk with dd) to the new LVM partition

> When I try to copy my own OS the file copy takes forever (only 20G) and my
> load average starts creeping up to 3+, which I assume may have to do with
> the fact that I'm running cp -ax / /mnt/guest01 which may loop copying
> /mnt/guest01 to itself or something similar?

"-x" should prevent that, but I don't think you need 20G for domU
anyway, so stay away from using bloated "template" (like your dom0).

> Anyways, long story short, is there a way to install to a partition via HTTP
> like with disk images?

In your case I'd actually recommend you try two things :
- try non-sparse file-based (or disk images, if you prefer that term)
vbd making sure that it uses tap:aio: instead of file:
- change your domU config file to say

disk = [ 'phy:/dev/VolGroup00/guest01,xvda,w', ]

You need this if you still want to use HTTP-install (e..g. using
virt-install or something similar). And drop the

root="/dev/xvda1"

line. You don't need it anyway.

> If not, what am I doing wrong using the prebuilt
> images?

>From your config file, I'd say Mike made a good point: you don't have an 
>initrd.
I'd rather not go into this yet though, because I'm not familiar with
jailtime.org images, and how you create them can make "best way to
create initrd" differ.

Regards,

Fajar

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