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

On 2012-6-25 10:10, Andrew Cathrow wrote: > > ----- Original Message ----- >> From: "Andy Grover" <agrover(a)redhat.com&gt; >> To: "Shu Ming" <shuming(a)linux.vnet.ibm.com&gt; >> Cc: libstoragemgmt-devel(a)lists.sourceforge.net, >> engine-devel(a)ovirt.org, "VDSM Project Development" >> <vdsm-devel(a)lists.fedorahosted.org&gt; >> Sent: Sunday, June 24, 2012 10:05:45 PM >> Subject: Re: [vdsm] [Engine-devel] RFC: Writeup on >> VDSM-libstoragemgmt integration >> >> On 06/24/2012 07:28 AM, Shu Ming wrote: >>> 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. >> OK my mistake, we don't pause the VM during live snapshot, we block >> on >> access to the luns while snapshotting. Does this keep live snapshots >> working and mean ovirt-engine can use libsm to config the storage >> array >> instead of vdsm? >> >> Because that was really my main question, should we be talking about >> engine-libstoragemgmt integration rather than vdsm-libstoragemgmt >> integration. > for snapshotting wouldn't we want VDSM to handle the coordination of > the various atomic functions? I think VDSM-libstoragemgmt will let the storage array itself to make the snapshot and handle the coordination of the various atomic functions. VDSM should be blocked on the following access to the specific luns which are under snapshotting.