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

[Yair Zaslavsky]

On 01/22/2012 09:26 AM, Livnat Peer wrote:
> 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.
Livnat - I think that in case of creating a template from snapshot we
should should have new API/Command, that will probably have lots in
common with Create VM 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.
+1 on Livnat's explanation - I do see a (design/implementation wise) an
option for some code reuse, but IMHO - this should be a new command with
new API modelling
> 
> 
> Livnat
> 
> _______________________________________________
> Engine-devel mailing list
> Engine-devel at ovirt.org
> http://lists.ovirt.org/mailman/listinfo/engine-devel