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From Tim Mackey <tmac...@gmail.com>
Subject Re: [DISCUSS] extending the libvirt/KVM plugin to also support libvirt/Xen
Date Mon, 09 Jun 2014 15:44:05 GMT
Dave,

Thanks for putting this up on the wiki. A few things jumped out at me...

- Please change "Xen" to "XenProject" or "Xen Project" as appropriate.
There's already a ton of confusion out there, and I'd like to see us
get our terms correct from the outset where ever possible.

- It would be good to see a UI mock up for how users would configure
the Xen Project hypervisor option.  I think that would go a long way
to helping with the mixed hypervisor cluster concept and how it could
be blocked.

- It would also be good to see examples of how the APIs might need to
be changed to support this.  Minimally I'd expect to see things like
supported disk/network/os types and that sort of thing.

- I see you have a todo to document the supported Xen Project
hypervisor and libvirt versions, but also dependencies on libxl
changes.  Are these critical dependencies, or if someone doesn't have
latest upstream will things work in a reduced feature set?

- C6.1 talks about exposing a config setting.  Is that really
required?  Couldn't that be set correctly based on hypervisor type?

- Would QCOW2 be used for the Xen Project disk type for all templates
to keep with KVM consistency?  I'm actually thinking  about support
for VMDK, but perhaps that's a different proposal?

- Since we're talking about sharing a libvirt plugin, I'm not clear on
if the shared work is done in a new libvirt plugin which is then
exposed to a KVM and a XenProject plugin or if the existing KVM plugin
is refactored to encompass both.

-tim




On Mon, Jun 9, 2014 at 2:35 AM, Wido den Hollander <wido@widodh.nl> wrote:
>
>
> On 06/08/2014 11:14 PM, Dave Scott wrote:
>>
>> Hi Wido,
>>
>> Thanks for your mail!
>>
>> On 8 Jun 2014, at 19:02, Wido den Hollander <wido@widodh.nl> wrote:
>>
>>> On 06/08/2014 06:23 PM, Dave Scott wrote:
>>>>
>>>> Hi,
>>>>
>>>> Following on from the earlier "[PROPOSAL] Support pure Xen as a
>>>> hypervisor”, I’ve added a design doc to the wiki:
>>>>
>>>>
>>>> https://cwiki.apache.org/confluence/display/CLOUDSTACK/Allow+hosts+running+the+Xen+hypervisor+to+be+managed+via+libvirt
>>>>
>>>> This design would allow people who want to manage their hypervisors
>>>> purely through the libvirt tools to choose the Xen hypervisor.
>>>>
>>>>  From the code point of view, I want to maximise sharing between the KVM
>>>> and Xen code paths, partly to make QA easier and partly to maximise the
>>>> chance that adding a feature for “Xen” causes it to work for “KVM”
and
>>>> vice-versa. In particular this means that, if a genuinely-useful capability
>>>> is currently missing from the libvirt libxl driver, I want to implement it
>>>> rather than work around it.
>>>>
>>>
>>> Seems like a great route to me! You also want to support Xen+Qemu with
>>> this way?
>>
>>
>> Yes, it should be possible to run fully virtualised VMs with Xen + Qemu. I
>> think we’ll be able to choose whether to run VMs as PV or HVM.
>
>
> Ok, but those will be different code paths at some level.
>
>
>>
>>> We have to be aware that there might be some storage differences between
>>> KVM and Xen like Ceph which is not fully supported yet by Xen.
>>
>>
>> Ceph is an interesting one. Xen itself doesn’t know anything about
>> storage— instead the dom0 takes care of it either via a kernel driver
>> (blkback) or userspace program (qemu or tapdisk). When I tried to make Ceph
>> work about a year ago[1] I hit a bug in libxl (the Xen control library). The
>> good news is the fix made it into Xen 4.4, so with luck we can get it to
>> work.
>>
>
> When Xen runs with Qemu as full HVM it's Qemu which takes care of the Ceph
> storage, so in that case it's fixed.
>
> I haven't got a lot of experience with PV Xen. I heard stories of Ceph being
> integrated in blktap(2), but never tested it.
>
>
>>
>>> If anything is missing in libvirt or the Java bindings we have to fix
>>> that indeed instead of hacking around it.
>>
>>
>> Great :)
>>
>> Cheers,
>> Dave
>>
>> [1]
>> http://xenserver.org/discuss-virtualization/virtualization-blog/entry/tech-preview-of-xenserver-libvirt-ceph.html
>>
>>>
>>> Wido
>>>
>>>> Comments appreciated!
>>>>
>>>> Cheers,
>>>> Dave
>>>>
>>>> [1]
>>>> http://mail-archives.apache.org/mod_mbox/cloudstack-users/201403.mbox/%3cCAJGXtBNbmQTQ81rALgH2kMA7V5WJYZKr3xnyasMKC_br+UKzOw@mail.gmail.com%3e
>>>>
>>
>

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