----- Original Message -----
From: "Shu Ming" shuming@linux.vnet.ibm.com To: "Federico Simoncelli" fsimonce@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).