On 06/25/2012 07:47 AM, Shu Ming wrote:
On 2012-6-25 10:10, Andrew Cathrow wrote:


----- Original Message -----
From: "Andy Grover" <agro...@redhat.com>
To: "Shu Ming" <shum...@linux.vnet.ibm.com>
Cc: libstoragemgmt-de...@lists.sourceforge.net, engine-de...@ovirt.org, "VDSM Project Development"
<vdsm-devel@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?

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 ?

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