[Engine-devel] [vdsm] RFC: Writeup on VDSM-libstoragemgmt integration

[Itamar Heim]

On 06/23/2012 03:09 AM, Andy Grover wrote:
> On 06/22/2012 04:46 PM, Itamar Heim wrote:
>> On 06/23/2012 02:31 AM, Andy Grover wrote:
>>> On 06/18/2012 01:15 PM, Saggi Mizrahi wrote:
>>>> Also, there is no mention on credentials in any part of the process.
>>>> How does VDSM or the host get access to actually modify the storage
>>>> array? Who holds the creds for that and how? How does the user set
>>>> this up?
>>>
>>> It seems to me more natural to have the oVirt-engine use libstoragemgmt
>>> directly to allocate and export a volume on the storage array, and then
>>> pass this info to the vdsm on the node creating the vm. This answers
>>> Saggi's question about creds -- vdsm never needs array modification
>>> creds, it only gets handed the params needed to connect and use the new
>>> block device (ip, iqn, chap, lun).
>>>
>>> Is this usage model made difficult or impossible by the current software
>>> architecture?
>>
>> what about live snapshots?
>
> I'm not a virt guy, so extreme handwaving:
>
> vm X uses luns 1&  2
>
> engine ->  vdsm "pause vm X"

that's pausing the VM. live snapshot isn't supposed to do so.

> engine ->  libstoragemgmt "snapshot luns 1, 2 to luns 3, 4"
> engine ->  vdsm "snapshot running state of X to Y"
> engine ->  vdsm "unpause vm X"

if engine had any failure before this step, the VM will remain paused. 
i.e., we compromised the VM to take a live snapshot.

> engine ->  vdsm "change Y to use luns 3, 4"
>
> ?
>
> -- Andy