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

----- Original Message ----- > > > ----- 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). I don't understand this, can you please elaborate why and in which case? The disk is plugged/unplugged? What happens when you commit? It becomes r/w? >> >> >> Livnat >> >> >> > > +1 for option 3 > +1 for option 3 as well (also good with option 1, but I think this will hinder usability).

Regards, Mike