[libvirt] Notes: Non-shared storage live migration w/ active blockcommit

This notes is based on an IRC conversation with Eric Blake, to have efficient non-shared storage live migration. Thought I'd post my notes here before I forget. Please review and spot if there are any inaccuracies. Procedure --------- (1) Starting from disk A, create a snapshot A <- A': $ virsh snapshot-create-as \ --domain f20vm snap1 snap1-desc \ --diskspec hda,file=/export/vmimages/A'.qcow2 \ --disk-only --atomic (2) Background copy of A to B: $ virsh blockcopy \ --domain vm1 vda /export/vmimages/B.qcow2 \ --wait --verbose --shallow \ --finish (3) Create an empty B' with backing file B: $ qemu-img create -f qcow2 -b B.qcow2 \ -o backing_fmt=qcow2 B'.qcow2 [or] $ virsh vol-create-as default B'.qcow2 1G \ --format qcow2 \ --backing-vol B.qcow2 --backing-vol-format qcow2 (4) Do a shallow blockcopy of A' to B': $ virsh blockcopy \ --domain vm1 vda /export/vmimages/B'.qcow2 \ --wait --verbose --shallow \ --finish (5) Then live shallow commit of B: $ virsh blockcommit \ --domain f20vm vda \ --wait --verbose --shallow \ --pivot --active --finish Block Commit: [100 %] Successfully pivoted -- /kashyap