Subject: Re: performance: domU in disk image or netboot from dom0 ?
To: None <joel@carnat.net>
From: Johan Ihren <johani@johani.org>
List: port-xen
Date: 04/24/2006 15:08:37
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Hi,

> I was wondering what was better (regarding performance) between using
> disk images for domU and just "netbooting" them from dom0 ?

I have no hard data on this as I haven't tested it. But both "work =20
fine" for a setup with a dozen [not too heavily utilized] VMs on a =20
single physical machine.

> My current configuration is:
> - every dom running NetBSD
> - system and pkgsrc in disk images (4Go)
> - data accessed by domUs from dom0 via NFS.
>
> My thinking configuration would be:
> - every doms running NetBSD
> - system, packages and data accessed by domUs from dom0 via NFS/=20
> netboot.
>
> any pros/cons ?
>
> Going further, as every domUs (or at least 99%) will be NetBSD's, what
> about using a single NFS shared system/packages via NFS with a =20
> layer for
> conf and temp files.
> Something like:
> domU1:
> 	dom0:/exports/domUs	/		nfs
> 	dom0:/exports/domU1	/mnt/specific	nfs
> 	/mnt/specific		/		union
> domU2:
> 	dom0:/exports/domUs	/		nfs
> 	dom0:/exports/domU2	/mnt/specific	nfs
> 	/mnt/specific		/		union
>
> binary updates are done (once) in dom0:/exports/domUs.
> each vmachine has it's own conf in dom0:/exports/domU*.
> sounds crazy ?

Yes ;-)

I think you'll spend more effort fighting the standard setup than it =20
is worth.

I ended up with sharing /usr/share + /usr/X11R6 + /usr/pkg via NFS =20
and the rest in machine specific images. That brought down the size =20
of the individual images to less than 200MB. But this is because I =20
need to be able to install local software on each machine. If that =20
isn't needed then you can probably share all of /usr and shrink =20
images to ~50MB.

Local config stuff I manage something =E0 la

for vm in $machines ; do
	copy template.img $vm.img
	mount $vm.img somewhere
	rsync $vm specific stuff into somewhere
	umount
done

Johan

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