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

----- Original Message ----- > From: "Livnat Peer" <lpeer(a)redhat.com&gt; > To: "Yair Zaslavsky" <yzaslavs(a)redhat.com&gt;, "Mike Kolesnik" > <mkolesni(a)redhat.com&gt; > Cc: engine-devel(a)ovirt.org > Sent: Thursday, January 19, 2012 9:19:52 AM > Subject: Re: [Engine-devel] Question about CloneVMFromSnapshot > feature in context of shared disks and direct > LUNs-based disks > > On 19/01/12 08:38, Yair Zaslavsky wrote: > > Hi all, > > Following the upstream meeting dated Wednesday January 18th, 2012 > > - > > I presented the clone VM from snpashot feature and we discussed > > the > > feature behaviour. > > > > Two issues that were raised are the behaviour of the feature in > > context > > of shared disks and direct LUNs-based disks - > > On one hand, if we copy&collapse such images - this may yield to > > data > > corruption (think of a scenario where the source and destination > > VMs use > > the same disk). > > On the other hand - if we decide not to copy&collapse - the > > target > > VM > > will have missing VM and its state will not totally reflect the > > logical > > state. > > One of the solution raises is to mark such disks (at the > > destination) as > > unplugged, allowing the administrator the ability to plug them > > (understanding of course the consequences). > > > > I would like to receive inputs on this issue > > > > > > Kind regards, > > > > Yair > > Hi Yair, > > Some clarifications on the above issue. > Currently when taking a snapshot on a VM with shared disks or > direct > LUN > disk there are 3 optional behaviors: > > 1. Blocking the snapshot action. (User can not take a snapshot of > the > VM > if it has plugged shared or direct LUN disks) > > 2. 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. > > 3. Taking the snapshot of the VM as is, leaving the VM > configuration > with plugged disks. > > > The issue with including these disks in the snapshot is that they > are > not really being snapshotted, they are not capturing the point in > time > we are trying to achieve in the snapshot. > > Enabling the snapshot action in such a state is a bit misleading to > the > user. > > If we do allow taking the snapshot we should mark the snapshot as > partial to indicate that the snapshot did not capture the point in > time > as the user intended. > > I have no preference with regards to the second and third approach, > the > second approach is a bit more safe, we basically force the user to > plug > the disks and be sure that he knows what he is doing and the third > approach is less safe and less annoying to the user (he took the > snapshot, cloned it and wants to start the VM - don't require extra > actions) > > Kolesnik - please note when starting VM in a preview mode we should > mount the disks in read-only mode (if supported).

> > > Livnat > > > +1 for option 3