[Engine-devel] Question about CloneVMFromSnapshot feature in context of shared disks and direct LUNs-based disks

[Livnat Peer]

On 20/01/12 17:21, Itamar Heim wrote:
> On 01/20/2012 12:01 PM, Livnat Peer wrote:
>> On 20/01/12 09:35, Ayal Baron wrote:
>>>
>>>
>>> ----- Original Message -----
>>>> Top Posting:
>>>>
>>>>  From user POV I think that option 2 is the only one that make sense.
>>>> We try to do as much as we can,
>>>> and on each "problematic" case, we make him aware and let him decide.
>>>>
>>>
>>> Yep, +1.
>>>
>>
>> Trying to get to a conclusion here,
>> 3 different people said on this thread that they think that from the
>> user perspective leaving the shared devices plugged is what they think
>> is the best behavior to the user. (Omer, Kolesnik, Yair)
>>
>> On the other hand we have 2 people who think that protecting the user is
>> more important than leaving the VM configuration as it was in the
>> original VM (Miki, Ayal).
>>
>> Ayal/Miki can you please specify what are we protecting the user from?
>>
>>
>> I think that because we are not snapshotting the shared disk and the
>> direct LUN they should not be part of the VM configuration (in the
>> snapshot) at all. we can not promise the user that the disk will be
>> there and if it is there we can not guarantee it is in the same state as
>> it was when we took the snapshot.
>>
>>
>> Another issue,
>>
>> I can not see a reason to limit this feature to creating a VM from
>> snapshot and not a template? Almost no extra work is needed for
>> supporting templates as well.
> 
> I assume you meant, creating a VM from another VM (if it is down)?
> It should be supported.

Actually I meant creating a Template from Snapshot.

What you suggested is creating a VM from VM.
Although I see how the two are connected, I think they should be modeled
as two different API calls.
There is a difference in the flow, behavior, locks and parameters
between the two.

Behavior:
- Original VM has to be down for creating a VM from VM, not the case for
creating a VM from snapshot.

parameters:
- Creating VM from snapshot should support getting a snapshot-ID,
Creating VM from VM get a VM id

Locks:
- When creating a VM from VM, we need to lock the original VM as a
whole, we can not edit the VM, take snapshot or any other VM level
action while such operation is active.
While for creating the VM from snapshot we can take more fine-grained
locks (only image related locks).

Implementation:
Well it is simply another implementation.


Livnat