[fedora-virt] Virtual Disk Setup

Anand Kumria wildfire at progsoc.org
Wed Jul 15 17:23:34 UTC 2009

On Wed, Jul 15, 2009 at 3:21 PM, Daniel P. Berrange <berrange at redhat.com>wrote:

> On Wed, Jul 15, 2009 at 10:12:16AM -0400, Rich Mahn wrote:
> > I am setting up several VMs using an F11 host.  Most of the VMs will
> > be F11 as well.
> >
> > >From earlier discussions on this list I recognize that the best
> > performance for virtual disks is with the backing storage on the host
> > being a parititon or LV.  Since I want some flexibility I will use
> > LVs, with virtio disks on most of the VMs.
> >
> > Here's my questions:
> >
> > 1. Each f11 VM needs three file systems--/boot, root, and swap
> >    (assuming you can call swap a file system).  Is it better to create
> >    three LVs (each) on the hosts, and treat it as three separate disks
> >    on the VMs?  Or is it better to just create one LV on the host and
> >    then divide up that virtual disk on the VM?
> There's no point separating /boot & root onto separate virtual
> disks.

Really? I have to admit to only being familiar with Xen, so I do not know if
this also applies to KVM-style virtualisation.

What I have found is that if you use pygrub (a minimal implementation of
grub written in Python) and attempt to boot a domain, it will have issues
unless /boot is a file.

Which has mean that I have made it separate to /, an LVM VG - for the
reasons you suggest.

Also - within the guest it wants to have a partition table and Xen, at
least, will simply have the devices /dev/sda1 and /dev/sda2 but not /dev/sda
which means grub (in the guest) complains.

Having /boot on a file based disk, with a parition table at the front, means
that /dev/sda is provided and that the guest is able to run grub without
hacking the device-map file (or temporarily make the device node, since it
will show up).

So, I'm one of "those people" looking to eventually migrate from Xen to KVM
-- is this issue all taken care of by KVM-style virtualisation?

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