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Re: [Xen-devel] Any plan to support disk driver domain?

On Fri, Jun 21, 2013 at 11:26:43AM +0800, G.R. wrote:
> On Tue, May 28, 2013 at 6:16 PM, Roger Pau Monné <roger.pau@xxxxxxxxxx> wrote:
> > On 04/04/13 12:26, G.R. wrote:
> >> Hi developers,
> >> I'm currently running a PVHVM freeNAS domU to serve storage (SATA
> >> controller passed-through) to all other domUs. However, some issues are
> >> observed in the network / NFS performance for the NAS domU.
> >> I noticed that there is a blkback driver in freebsd which is documented
> >> as capable to export disk to other domains, which looks very promising.
> >> However, the wiki says that disk driver domain is not supported (at
> >> least for now).
> >>
> >> I wonder if there is any plan to support such disk driver domain? It'll
> >> be a great feature for my use case.
> >
> > I've added a tutorial that explains how to use storage driver domains
> > with Xen 4.3, it contains a FreeBSD section that explains how to use ZFS
> > ZVOLS as disk backends for other domains, see:
> >
> > http://wiki.xen.org/wiki/Storage_driver_domains
> >
> Hi Roger,
> I just checked out your wiki page and it seems to be a fairly simple setup.
> It looks like a miracle that the freebsd version does not require
> those helper utils.
> As I understand from what Daniel stated in his mail, the linux driver
> domain would
> rely on some hotplug scripts delivered with xen to hook up the connection.
> I was imagining some similar sciprts will need to be hooked into
> FreeBSD devd in similar manner.
> How does it work without these? I'm not familiar with the FreeBSD kernel.
> Also, does it has any assumption on the FreeBSD version? I'm on 8.3.1,
> which is a kind of old but still PVHVM capable.
> In your example, the driver is setup using zvol. I wonder if there are
> any constraint prohibiting using a file based backend?
> Finally, I saw this limitation in the wiki:
> >> It is not possible to use driver domains with pygrub or HVM guests yet, so 
> >> it will only work with PV guests that have the kernel in Dom0.
> While I can imagine why pygrub does not work, I don't understand the
> reason HVM is affected here. Could you explain a little bit?
> And what about a HVM with PV driver? (e.g. those windows guests)

It needs the backends. That means you can do it with PVHVM or with PV guests.

> Thanks,
> Timothy
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