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

2012-06-24 Thread Shu Ming 

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.





engine -  libstoragemgmt snapshot luns 1, 2 to luns 3, 4
engine -  vdsm snapshot running state of X to Y
engine -  vdsm unpause vm X


if engine had any failure before this step, the VM will remain paused. 
i.e., we compromised the VM to take a live snapshot.



engine -  vdsm change Y to use luns 3, 4

?

-- Andy


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--
Shu Ming shum...@linux.vnet.ibm.com
IBM China Systems and Technology Laboratory


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

2012-06-24 Thread Andrew Cathrow 


- 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?
 
 Thanks -- Regards -- Andy
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