----- Original Message -----
> From: "Shu Ming" <shum...@linux.vnet.ibm.com>
> To: "Federico Simoncelli" <fsimo...@redhat.com>
> Cc: "VDSM Project Development" <vdsm-devel@lists.fedorahosted.org>
> Sent: Tuesday, February 7, 2012 4:00:39 PM
> Subject: Re: [vdsm] Live Merge and Storage Live Migration
> Another question about the Storage Live Migration wiki page, in the
> Engine-VDSM flow:
> createVolumeCrossSD():
>   domain1: [base(raw)]<-[snap1(qcow2)]<-+-(VM)
>   domain2:                              +-[snap2(qcow2)]
> blockMigrate():
>   domain1: [base(raw)]<-[snap1(qcow2)]<-+
>   domain2:                              +-[snap2(qcow2)]<-(VM)
> I think there must have a storage quiesce time between the snap2
> creation and setting the VM on top of snap2.
> When the snap2 is being created, VM cannot access snap1. Only after
> VM is set on top of snap2, the quiesce period is end.

That is not required. The snap2 is there as place-holder (it doesn't
hold any internal state about snap1). We need to do so because the lvm
volume must be created on the SPM.

After that the qemu-kvm re-initialize the qcow header in snap2 (hopefully
fixing BZ#785683 too).

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