[Engine-devel] SharedRawDisk feature detail

[Livnat Peer]

On 14/02/12 11:44, Maor wrote:
> On 02/14/2012 09:17 AM, Livnat Peer wrote:
>> On 13/02/12 19:44, Maor wrote:
>>> On 02/12/2012 07:03 PM, Livnat Peer wrote:
>>>> On 02/02/12 17:15, Maor wrote:
>>>>> Hello all,
>>>>>
>>>>> The shared raw disk feature description can be found under the following
>>>>> links:
>>>>>   http://www.ovirt.org/wiki/Features/DetailedSharedRawDisk
>>>>>   http://www.ovirt.org/wiki/Features/SharedRawDisk
>>>>>
>>>>> Please feel free, to share your comments.
>>>>>
>>>>> Regards,
>>>>> Maor
>>>>> _______________________________________________
>>>>> Engine-devel mailing list
>>>>> Engine-devel at ovirt.org
>>>>> http://lists.ovirt.org/mailman/listinfo/engine-devel
>>>>
>>>> Hi Maor,
>>>>
>>>> - "when taking a VM snapshot, a snapshot of the shared disk will not be
>>>> taken."
>>>> I think it is worth mentioning that the shared disk will be part of the
>>>> VM snapshot configuration. The disk will appear as unplugged.
>>> Agreed, I changed it to the following:
>>> when taking a vm snapshot, a snapshot of the shared disk should not be
>>> taken, although it will be part of the VM snapshot configuration and the
>>> disk will appear as unplugged.
>>>>
>>>> - Move VM is deprecated in 3.1.
>>> Right, I removed this anecdote from the wiki.
>>>>
>>>> - It seems from the wiki that shared disk is not supported for template
>>>> but is supported for VM pool.
>>>> I am not sure how can we do that? iirc we create pool from template.
>>> What I was thinking about, is that the administrator can take a VM from
>>> the pool and attach it a shared disk, after the VM was created (for
>>> testing).
>>>
>>> The motivation for adding shared disk was that each entity that can be
>>> added with a disk can also be added with shared disk.
>>> Today, Administrator can add a disk to a VM from pool, which might be
>>> wrong behaviour, so maybe its better not to support it...
>>>>
>>>> What is the complexity of supporting shared disk in Templates? off the
>>>> top of my head it seems like it is more complicated to block shared
>>>> disks in templates than to support it. What do you think?
>>> Implementation wize it might be less complex, the problem is the use
>>> cases it raises, 
>>> some of them which I'm thinking about are:
>>> * If the disk will be deleted from the DC, should we remove it from the
>>> template? or leave an indication in the template that there was a shared
>>> disk there, maybe should not allow to delete the disk in the first
>>> place, until it is unattached from the template?
>>
>> Since template configuration is 'read-only' you can not change a disk to
>> be plugged or unplugged.
>> I would say you can not delete a disk that is part of a template
>> regardless if it is shared or not.
> So in that case template with shared disk, will block the user from
> removing the shared disk from the DC.
> Won't it will make the flow for the user a bit complicated.
> User who wants to remove the shared disk, will need to remove the VM's
> which are based on the template and then remove the template it self.

I see the complication of delete, we have similar complications for
delete regardless of shared disk (deleting disk with snapshots).

Other than delete can you think of other complicated scenarios?

>>
>>> * What do we want to do when creating a template from VM with shared
>>> disk - Should User choose whether to create a template with/without the
>>> shared disk?
>>>
>>
>> If a user is creating a template from VM the configuration should be
>> identical to the VM.
>>
>>> Blocking shared disk from template means creating the template without
>>> the shared disk, the implementation for it is to check if the disk is
>>> shared or not.
>>> I think that if GUI will support attaching shared disk to multiple VMs,
>>> there is no strong use case for allowing adding shared disk to a template.
>>
>> I am not sure what the above comment means but remember that we have API
>> users as well as UI.
>>
>> I think that if we don't have a strong case for not supporting shared
>> disk in templates the default should be to support it.
>>
>>>>
>>>> Livnat
>>>>
>>
>