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Re: [Xen-users] Diskless Xen (PXE, NFS, ...)

To: Thomas Treutner <thomas@xxxxxxxxxx>
Subject: Re: [Xen-users] Diskless Xen (PXE, NFS, ...)
From: Marcel van Dorp <M.vanDorp@xxxxxxx>
Date: Wed, 28 Oct 2009 17:12:44 +0100
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Thomas Treutner wrote:
> Hello,
> I'd like to ask if someone has experience with setting up Xen (I use 3.2 from 
> Lenny) in a diskless scenario - so not just the DomUs on a central storage 
> (therefore, I use open-iscsi), but also Xen itself and the Dom0? 
> I tried that because it would make adding nodes and other changings quite 
> easy, and save disks. I used PXE (with mboot.c32) and NFS-Root, and it worked 
> quite well after building a nfsroot capable initrd and considering that the 
> network device used for nfsroot is not usable for building a bridge (without 
> some initramfs customizations, I read) because the link will be lost when the 
> bridge comes up.
> But when I tried to live migrate DomUs between the nodes, I faced severe 
> troubles. Migrations failed because, AFAIR, the block device frontend 
> couldn't be disconnected? After that, I couldn't even get block device stats 
> from libvirt...
> Has anyone done such a setup, preferrably even with iSCSI, but without 
> dedicated hardware such as HBAs etc.? Or does someone know a link to a howto? 
> I've searched the mailing list and Google quite some time, and surprisingly, 
> most people care only about central storage for domUs...

This is almost exactly what I am trying to do, except voor the NFS Root
part. I want all to be available n the iSCSI storage and the virtual
environment, and that means my NFS server is also a virtual one. That
must be up to be able to start Dom0, but I need Dom0 to start the DomU
actins as the NFS server.... So I choose to do the latter:

I've built a Xen3.2 live install on a USB disk, and use that as the
local storage for Dom0. I do have HBAs, but for now, I cannot use the
hardware iSCSI support, because the driver is not yet available for my
current kernel.

The storage is indeed iSCSI, with the open-iSCSI initiator (also in the
initrd). For the DomUs, I use a nilfs partition on the iSCSI storage, so
this can be shared by the different Dom0s.

I'm still in the development phase of this setup. I am also considering
to put the Dom0 root on iSCSI, just leaving the kernel and initrd on the
USB disk. The final step is migrating to iSCSI boot, as soon as the
drivers become available. Putting that on a PXE server should be easy to

As I was saying, I'm still developing this, and I did not yet reach the
point of live migration of DomUs. You know, normal work also continues....

The next 2 weeks I'm working somewhere else, putting this on the
low-priority list...

Hope this helps,


> tia & kr,
> tom
> _______________________________________________
> Xen-users mailing list
> Xen-users@xxxxxxxxxxxxxxxxxxx
> http://lists.xensource.com/xen-users

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ing. Marcel van Dorp (CCDP, CCNP, CCSP)
WiWo Support                                 http://www.wiwo.nl
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2340 BB Oegstgeest                           gsm  0653-50 77 76
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