Re: [Engine-devel] the future of template cloning

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.

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.