On 01/19/2012 08:41 PM, Miki Kenneth wrote:
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.
Miki Miki, just to clear /be sure - you're talking about taking the snapshot as is, living the shared disk as "plugged" on destination VM?
Yair
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From: "Ayal Baron" <abaron@redhat.com> To: "Yair Zaslavsky" <yzaslavs@redhat.com> Cc: engine-devel@ovirt.org Sent: Thursday, January 19, 2012 4:04:02 AM Subject: Re: [Engine-devel] Question about CloneVMFromSnapshot feature in context of shared disks and direct LUNs-based disks
----- Original Message -----
On 01/19/2012 10:32 AM, Mike Kolesnik wrote:
----- Original Message -----
----- Original Message -----
From: "Livnat Peer" <lpeer@redhat.com> To: "Yair Zaslavsky" <yzaslavs@redhat.com>, "Mike Kolesnik" <mkolesni@redhat.com> Cc: engine-devel@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).
I agree with Mike - I think option one is too "aggressive" in protecting us, this is why I prefer 3. +1 on option 3
This would only be acceptable if the disk is marked read only. Just leaving the disk plugged means many users *will* corrupt their VMs. That trumps the need to mark a checkbox if you want it available.
As I said before, readonly has its own problems and in fact, IMO the behaviour is even more difficult to explain (yeah, you might corrupt the running VM if it's r/w so we made it r/o and now if you start up your clone / preview you will get a kernel panic).
Regards, Mike
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