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On Thu, Feb 23, 2017 at 7:18 PM, Zhenyu Zheng <zhengzhenyulixi at gmail.com>
wrote:

> Matt,
>
> Thanks for the information, I will check that; But still I think the user
> demand here is to use local disk from
> compute node as block device, as the data can be remained if the old vm
> got deleted, and we can start a
> new one with the data and having the performance they wanted.
>
> Kevin Zheng
>
> On Fri, Feb 24, 2017 at 4:06 AM, Matt Riedemann <
> mriedem at linux.vnet.ibm.com> wrote:
>
>> On 9/26/2016 9:21 PM, Zhenyu Zheng wrote:
>>
>>> Hi,
>>>
>>> Thanks for the reply, actually approach one is not we are looking for,
>>> our demands is to attach the real physical volume from compute node to
>>> VMs,
>>> by this way we can achieve the performance we need for usecases such as
>>> big data, this can be done by cinder using BlockDeviceDriver, it is quite
>>> different from the approach one you mentioned. The only problem now is
>>> that we cannot practially ensure the compute resource located on the same
>>> host with the volume, as Matt mentioned above, currently we have to
>>> arrange 1:1 AZ in Cinder and Nova to do this and it is not practical in
>>> commercial
>>> deployments.
>>>
>>> Thanks.
>>>
>>>
>> Kevin,
>>
>> Is the issue because you can't use ephemeral local disks (it must be a
>> persistent boot from volume)?
>>
>> Have you looked at using the LVM image backend for local storage in Nova?
>> I thought cfriesen said once that windriver is doing high performance
>> config using local LVM in nova.
>>
>> --
>>
>> Thanks,
>>
>> Matt Riedemann
>>
>>
>>
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> Hi Kevin,

Few things that may be related to your request:

>>"our demands is to attach the real physical volume from compute node to
VMs"

Cinder had this capability for a while in the form of the block-driver, but
it's been removed due to lack of functionality, testing and really interest
all the way around.  We also took a look at performance data and the fact
was that the performance between iSCSI over a 10Gig dedicated network and a
local block device was minimal.  The block-driver model breaks just about
every Cinder feature at this point so rather than carry it around as a
special one off case it's been removed and if you really need local disk to
the compute node, you need to just use the ephemeral LVM driver in Nova.

>>"compute node as block device, as the data can be remained if the old vm
got deleted"

Yes, I understand what you are asking for here, and that's similar to how
the old block-driver worked; like I said though that's been deprecated and
removed.  I would be curious to get more info about the *requirement* here
in terms of performance.  We had a number of people look at the performance
characteristics between a Cinder LVM Volume behind an LIO Tgt and found
there to be minimal differences in performance between the raw disk device
without iSCSI.

There are ways to bring the block-driver up to feature parity etc, but
frankly most have decided it's not worth it as there's very little real
benefit to using it over the existing and well supported drivers.

Thanks,
John
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