Re: [Kimchi-devel] Rethink the Relationship of Template and VM

Would anyone share some background information on why we implement LUN in template? I want to know the original author's considerations. I googled this topic in the mail list, didn't get much context information.

on 2014/04/28 21:08, Sheldon wrote: > On 04/28/2014 01:45 PM, Mark Wu wrote: >> On 04/27/2014 10:38 PM, Zhou Zheng Sheng wrote: >>> Hi all, >>> >>> I'm working on host device passthrough. A a problem troubles me: I see >>> in current Kimchi code, when adding a specific SCSI or iSCSI LUN, it is >>> added to the template but not the VM. This is counter-intuitive, because >>> a template is to store the common information for lots of VMs, while a >>> specific LUN should only be used by just one VM. It's OK for DIR, NFS >>> and Logical storage pool being managed by the template, because actually >>> the template allocates a new specific volume for a new VM, so the >>> specific volume goes with the specific VM but not the template. Since we >>> don't define a specific DIR storage volume in the template, why we >>> define a concrete LUN in it? >>> >>> The first problem in the current design is that we can not attach a new >>> LUN to a VM after the VM is created. >>> >>> Another problem is that we mix the "things in common" and "things >>> special" in template, thus we make its responsibility complex. Static >>> and dynamic validations are also mixed in template. >>> >>> The third problem is that if we get 10 LUNs for 10 VMs, the user has to >>> create 10 templates at first, then create 10 VMs from the 10 templates >>> respectively. It's a bit tedious. >>> >>> The fourth problem is that if a LUN is used by a VM, usually it should >>> not be used by other VMs, so it implies that by specifying a LUN in a >>> template, the template should only create just one VM. What's the point >>> to make a template that only produces one VM? >>> >>> It seems a cleaner way is putting SCSI LUN handling code in VM. Firstly, >>> we can assign a SCSI/iSCSI storage pool to the template. When it's time >>> to create a VM from the template, Kimchi lists all the available LUNs in >>> the storage pool and the user can just pick some LUNs. The VM override >>> parameters are suitable to store the LUNs information. It also makes >>> possible to implement some mechanisms to add/remove LUNs after a VM is >>> created, which is a very typical user requirement. >>> >>> The same problem exists in host device passthrough. For a specific >>> device, it should be passthrough to a specific VM but not a template >>> I'd like to collect some thoughts before my device passthrough patch V2. >>> In which place you'd suggest me to put device passthrough information, >>> template or VM? >> Template should NOT include any vm specific information. As I mentioned >> in the comments of your pci passthrough patch, we need allow user have >> chance to customize the configuration when creating vm based on >> template. > ACK