[Engine-devel] SharedRawDisk feature detail

[Maor]

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.
> 
>> * 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
>>>
>