----- Original Message ----- > > > ----- Original Message ----- > > > > > > ----- Original Message ----- > > > From: "Livnat Peer" <[email protected]> > > > To: "Yair Zaslavsky" <[email protected]>, "Mike Kolesnik" > > > <[email protected]> > > > Cc: [email protected] > > > 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)
-1, user should be able to take snapshots. Note that once we have integration with hardware side snapshots, we will be able to snapshot direct LUNs (when supported). > > > > > > 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. +1, user has to specifically say 'I know that the direct LUN is not in the same state as it was when I took the snapshot but I know what I'm doing and I want to run the snapshot with the LUN as is' > > > > > > 3. Taking the snapshot of the VM as is, leaving the VM > > > configuration > > > with plugged disks. -1, this will lead to accidental corruptions. > > > > > > > > > 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. +1, the user should be aware of what she did. > > > > > > 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). Note that if the LUN contains a file system to be mounted and the disk is plugged in read only mode the guest will likely have a kernel panic when trying to mount the fs, I'm not sure this is the behaviour we want. > > 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? No, you mark it as read-only in the configuration when you create the snapshot. User would have to manually change this to r/w. I'm not sure we should both mark it as unplugged and r/o (although this is the safest option). As it would be annoying to get the disk to actually work in r/w (plug + make r/w). Andy, your thoughts on this? > > > > > > > > > > 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 > _______________________________________________ > Engine-devel mailing list > [email protected] > http://lists.ovirt.org/mailman/listinfo/engine-devel > _______________________________________________ Engine-devel mailing list [email protected] http://lists.ovirt.org/mailman/listinfo/engine-devel
