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

[Shu Ming]

On 2012-6-23 20:40, Itamar Heim wrote:
> 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.

Tough we don't expect to do a pausing operation to the VM when live 
snaphot is undergoing, the VM should be blocked on the access to 
specific luns for a while.  The blocking time should be very short to 
avoid the storage IO time out in the VM.

>
>> 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
>
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-- 
Shu Ming <shuming at linux.vnet.ibm.com>
IBM China Systems and Technology Laboratory