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

[Miki Kenneth]

----- Original Message -----
> From: "Ayal Baron" <abaron at redhat.com>
> To: "Miki Kenneth" <mkenneth at redhat.com>
> Cc: engine-devel at ovirt.org, "Itamar Heim" <iheim at redhat.com>
> Sent: Friday, January 20, 2012 1:37:54 PM
> Subject: Re: [Engine-devel] Question about CloneVMFromSnapshot feature in	context of shared disks and direct
> LUNs-based disks
> 
> 
> 
> ----- 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 :)
Of course, this is no acceptable!
> 
> > 
> > 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?
Don't know, will try to find out.
> 
> > 
> > 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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> > Engine-devel at ovirt.org
> > http://lists.ovirt.org/mailman/listinfo/engine-devel
> > 
>