[Engine-devel] Question about CloneVMFromSnapshot feature in context of shared disks and direct LUNs-based disks

[Miki Kenneth]

Sorry guys if I was not clear or maybe I missed something...

Let's take a use case:
- User like to create a VM for instance Win 2008, and would like to attach a shared disk to it.
- User liked to create multiple copies of this VM.
(all vms shared the same disk, and run same OS).
so do I do that in oVirt.... we can do either option 2 or 3.

Option 2 as I read it:
Taking the snapshot and marking the shared disk and direct LUN
disks as unplugged (in the VM snapshot configuration) and marking the snapshot state as partial.

my understanding was:
1. we is clone the vm configuration as is.
2. we try to clone the different disks
3. if there is shared raw disk/direct LUN, we do not clone them, we "unplug" them.
4. the (poor) user, will have to plug these vms manually, in order to assure connectivity and raise awareness that these disks are "special". This is nice but not great.

Option 3 as I read it:
Taking the snapshot and marking the shared disk and direct LUN
disks as plugged (in the VM snapshot configuration) and marking these disks as read only.

my understanding was:
1. we is clone the vm configuration as is.
2. we try to clone the different disks
3. if there is shared raw disk/direct LUN, we do not clone them , we make them read only(?), and they remain plugged.
4. user is happy.
5. only issue is how we have to make the user aware that these disks are shared/read only???
if this is possible, I agree to vote for third option :)

You might want to have a look at:
http://www.symantec.com/connect/articles/building-vmware-shared-disk
(look at the configuration file in Vmware:
disk.locking = "FALSE"
diskLib.dataCacheMaxSize = "0"
#scsi1 data storage
scsi1.present = "TRUE"
scsi1.virtualDev = "lsilogic"
scsi1.sharedbus = "none"
scsi1:0.present = "TRUE"
scsi1:0.fileName = " D:\Virtual Machines\Shared Disk\SHARED-DISK.vmdk "
scsi1:0.mode = "independent-persistent"
scsi1:0.shared = "TRUE"      
scsi1:0.redo = ""
The shared flag is set for shared file, indicating "no locking"

I would like to re-ephasize that the user does not know the snapshotting mechanics. He would like to "copy" the VM as is. We have to do our best, and highlights the issues/sensitive points he has to take care of. 


does that make sense?

Miki



----- Original Message -----
> From: "Itamar Heim" <iheim at redhat.com>
> To: "Livnat Peer" <lpeer at redhat.com>
> Cc: engine-devel at ovirt.org
> Sent: Friday, January 20, 2012 7:21:34 AM
> Subject: Re: [Engine-devel] Question about CloneVMFromSnapshot feature in context of shared disks and direct
> LUNs-based disks
> 
> On 01/20/2012 12:01 PM, Livnat Peer wrote:
> > On 20/01/12 09:35, Ayal Baron wrote:
> >>
> >>
> >> ----- Original Message -----
> >>> Top Posting:
> >>>
> >>>  From user POV I think that option 2 is the only one that make
> >>>  sense.
> >>> We try to do as much as we can,
> >>> and on each "problematic" case, we make him aware and let him
> >>> decide.
> >>>
> >>
> >> Yep, +1.
> >>
> >
> > Trying to get to a conclusion here,
> > 3 different people said on this thread that they think that from
> > the
> > user perspective leaving the shared devices plugged is what they
> > think
> > is the best behavior to the user. (Omer, Kolesnik, Yair)
> >
> > On the other hand we have 2 people who think that protecting the
> > user is
> > more important than leaving the VM configuration as it was in the
> > original VM (Miki, Ayal).
> >
> > Ayal/Miki can you please specify what are we protecting the user
> > from?
> >
> >
> > I think that because we are not snapshotting the shared disk and
> > the
> > direct LUN they should not be part of the VM configuration (in the
> > snapshot) at all. we can not promise the user that the disk will be
> > there and if it is there we can not guarantee it is in the same
> > state as
> > it was when we took the snapshot.
> >
> >
> > Another issue,
> >
> > I can not see a reason to limit this feature to creating a VM from
> > snapshot and not a template? Almost no extra work is needed for
> > supporting templates as well.
> 
> I assume you meant, creating a VM from another VM (if it is down)?
> It should be supported.
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