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

[Ayal Baron]

----- Original Message -----
> 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.

Correct 

> 
> 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 :)

This will become apparent to the user once he boots the machine and gets the kernel panic :)

> 
> 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"

This is shared disk, what about RDM?

> 
> 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.
> > _______________________________________________
> > Engine-devel mailing list
> > Engine-devel at ovirt.org
> > http://lists.ovirt.org/mailman/listinfo/engine-devel
> > 
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