Re: [Xen-users] stateless dom0

[Javier Guerra <javier@xxxxxxxxxxx>]

On Thu, Mar 19, 2009 at 2:50 AM, Denis J. Cirulis <denis@xxxxxxxxxxxxx> wrote:
> Hello,
>
> I'm trying to setup stateless dom0 host image.
> The idea is to make dom0 host diskless booted off storage/pxe. What are
> the best practices of making such a setup ?
> I already tried nfs-root iscsi-root and aoe-root all these setups works
> perfect, what about making xen running rootless I mean in ramdisk ?

most loaders (including PXE):

- load kernel + initrd:
- initrd is small, compressed and R/O (maybe cramfs)
- on initrd there's a startup script that loads some extra kernel
modules, mounts other filesystem, does a pivot/root and continues with
another script on the new root
- the new script does the rest of the work, and unmounts the initrd.

but.... there's no hard rule about what the startup script on the
initrd _must_ do.  you can easily build a complete system on initrd,
one that:

- loads all needed modules (not just the few needed to mount the next root)
- mounts a few writeable directories (either tmpfs or nfs) on /var,
/tmp, /log, etc
- starts xen daemons
- launches any DomU

i wouldn't call it 'rootless' but 'initrd based'.  well done, it makes
all boxes really interchangeable and reduces the load on NFS servers.

i'm not sure if it's much better than iSCSI or AoE for root, but might
reduce duplications. (since it's 'more natural' to mount initrd as
R/O)

-- 
Javier

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