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

[Andrew Cathrow]

----- Original Message -----
> From: "Andy Grover" <agrover at redhat.com>
> To: "Shu Ming" <shuming at linux.vnet.ibm.com>
> Cc: libstoragemgmt-devel at lists.sourceforge.net, engine-devel at ovirt.org, "VDSM Project Development"
> <vdsm-devel at lists.fedorahosted.org>
> 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?
> 
> Thanks -- Regards -- Andy
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