Re: [Xen-users] File system layout

[Paul Barnett <xen@xxxxxxxxxxxxxxx>]

On Mon, 17 Mar 2008, Fajar A. Nugraha wrote:

> Mark Williamson wrote:
> > > My supervisor wants to create a LV then give that to a VM and then
> > > create a VG with LV's under it inside the VM. I have read on the list
> > > where this will give bad performance inside the VM.
> > It won't necessarily give *bad* performance but doing the two layers of 
> > translation is a bit unfortunate.
> An email from Sadique on this list sometime early this year said LVM has 2%
> performance hit over pysical partitions. So using LVM on both dom0 and domU 
> (roughly) reduce performance by 4%.
> > To me, the simplicity of doing all LVM management in dom0 and hiding it 
> > from the guest appeals. 
> > It's actually possible to pass separate LVM volumes to appear as individual 
> > partitions in the guest - this has the advantage that there's no MS-DOS 
> > partition table to worry about, just a load of linear LVs with filesystems 
> > on.
> I second that. That is what we do for Linux PV guests.
For interest, how do you do this?

I can see how you can make dom0 lvs appear to the pv guest as separate
disks, and mke2fs each as a whole-disk file-system (without a
partition table.) But is there some trick to make separate dom0 lvs
appear to the domu guest as partitions on a single disk? If so, where
is the partition table, and where does grub install to?

Or, assuming separate disks, where does /boot go?

Do you make a small (100M) lv for /boot?

and how do you tell grub to boot from it - I tried it, and grub does not
seem able to install itself correctly - I get:

[root@domu ~ 0]$ grub-install /dev/hda
Unknown partition table signature
Unknown partition table signature
Unknown partition table signature
Unknown partition table signature
Unknown partition table signature
The file /boot/grub/stage1 not read correctly.
[root@domu ~ 1]$

Am I missing something obvious?

(using Centos 5.1 x86_64 as dom0 and domu)




> Regards,
>
> Fajar
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