[Engine-devel] SharedRawDisk feature detail

[Livnat Peer]

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.

> * 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
>>