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Re: [fedora-virt] Virtual Disk Setup





On Wed, Jul 15, 2009 at 3:21 PM, Daniel P. Berrange <berrange 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?

Regards,
Anand

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