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

* Andrew Cathrow&lt;acathrow(a)redhat.com&gt; [2012-06-24 21:11]: > > ----- Original Message ----- >> From: "Andy Grover&quot;&lt;agrover(a)redhat.com&gt; >> To: "Shu Ming&quot;&lt;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? Absolutely. Requiring every management application (engine, etc) to integrate with libstoragemanagement is a win here. We want to simplify working with KVM, storage, etc not require every mgmt application to know deep details about how to create a live VM snapshot.