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

[Javier Guerra <javier@xxxxxxxxxxx>]

On Wed, Oct 28, 2009 at 1:45 PM, Thomas Treutner <thomas@xxxxxxxxxx> wrote:
> On Wednesday 28 October 2009 17:07:39 Javier Guerra wrote:
>> - be sure to initiate the iSCSI devices on Dom0.  IOW, the DomU's
>> won't know their storage isn't local.
>
> Yep, I did it that way, using a block-iscsi script floating around in the
> Internet somewhere and then iscsi: instead of phy: etc.

you can keep the phy: if you attach the iSCSI devices to all Dom0's.
that way, for Xen the LUNs are just block devices.  i have no idea if
that implies more (or less) overhead, though.

>> - you can get rid of NFS totally, either put your Dom0 in iSCSI too,
>
> I've searched for that, it seems to be quite a hack without HBAs to me, even
> for vanilla kernels.

no need for special hardware; just put the iSCSI drivers in your
initrd and do the LUN attaching before switching roots (and after
setting up the bridge).

>> or just keep the initrd.  there's no requirement for initrd to yield
>> to another root.  in either case, you'll find it much easier to
>> manage.
>
> Hm, that would be interesting. So the Dom0 would reside in a ramdisk? Wouldn't
> one need quite some (additional) amounts of RAM for that? I have a node with

a small linux distro fits in less than 30MB of disk (even less if you
use busybox instead of the full GNU tools) and if you use cramfs for
the initrd, you can keep it compressed while mounted in RAM.  the Xen
daemons aren't too big either.  the biggest requirement is Python,
IFRC.

> just 2G which isn't very much for Xen anyways, when subtracting 256-512M for
> Dom0. And I think I would need something like NFS anyways for the DomU.cfgs,
> if I don't want to regenerate the initrds every time.

you could fetch the configs from a central config server via http, or
tftp... makes you less dependent on the continued availability of the
network  (significant only if iSCSI is on a separate network)


-- 
Javier

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