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

["G.R." <firemeteor@xxxxxxxxxxxxxxxxxxxxx>]

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)

Thanks,
Timothy

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