[Engine-devel] the future of template cloning

[Itamar Heim]

On 01/12/2012 06:47 PM, Ewoud Kohl van Wijngaarden wrote:
> On Thu, Jan 12, 2012 at 05:50:56PM +0200, Itamar Heim wrote:
>> On 01/12/2012 04:04 PM, Ewoud Kohl van Wijngaarden wrote:
>>> On Thu, Jan 12, 2012 at 03:56:05PM +0200, Itamar Heim wrote:
>>>> On 01/12/2012 03:50 PM, Jon Choate wrote:
>>>>>> On Thu, Jan 12, 2012 at 8:44:56PM, Itamar Heim wrote:
>>>>>> On 01/12/2012 02:19 PM, Jon Choate wrote:
>>>>>>> We are going to be able to store the disks for a template on
>>>>>>> different storage domains due to the multiple storage domain
>>>>>>> feature.  Cloning a template will still be possible, but will it
>>>>>>> provide any value?  Thoughts?
>>>>>>
>>>>>> you would want to clone the disks to the storage domains you would
>>>>>> want to create thinly provisioned disks from for this template.
>>>>>>
>>>>>> so a template could have disk1 and disk2 on SD1, then disk2 cloned to
>>>>>> SD2 to allow creating a VM with thin COW for disk2 on SD2 as well.
>>>>>>
>>>>>
>>>>> But with the ability to create a template with disk 1 on SD1 and
>>>>> disk2 on SD2 is that still a compelling feature?
>>>>
>>>> yes, since I may want to create virtual machines from this template
>>>> where the 2nd disk is sometimes on SD1 and sometime on SD2 (just
>>>> like today, where i can instantiate a VM from the template on
>>>> multiple storage domains)
>>>> The new feature will just allow me to not clone all the disks of the
>>>> template to all storage domains, rather a subset.
>>> But would this be interesting to the user or would it be better to do
>>> this transparently so the user doesn't have to care? The user just wants
>>> to use template X and store it on storage domain Y with COW. The system
>>> could deduce it has to be cloned first and not bother the user.
>>
>> that means a user would be able to affect where the template
>> resides. user may not have permissions to do so, would require to
>> configure which quota this will happen from, etc.
>> so I'm not sure doing it implicitly based on a user trying to create
>> a disk on a domain.
> For my point of view I assume templates are immutable so a copy only
> wastes space but I don't see how that matters in this case. If the user
> has no permission to copy a template, [s]he has to make full copy of the
> template to create the VM anyway. Making a copy and then create a thin
> COW VM consumes the same amount of space with as benefit that additional
> VMs based on the template can also use COW.

my point is there would be a difference between the admin pre-populating 
the template on the storage domains they wish to allow thinly 
provisioned VMs from it, from the admin quota.

>
> Side note: I haven't at oVirt and my experience is based on RHEV 2.2, so
> maybe I've overlooking several new features that would limit this.