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

On 06/25/2012 07:47 AM, Shu Ming wrote: > 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. I kind of agree. If snapshot is being done at the array level, then the array takes care of quiesing the I/O, taking the snapshot and allowing the I/O, why does VDSM have to worry about anything here, it should all happen transparently for VDSM, isnt it ?