On Thu, Sep 25, 2014 at 07:56:09PM +0530, Kashyap Chamarthy wrote:
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.
Noting a couple of things I missed. . .
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
Before performing a live blockcopy, make the domain transient (as persistent dirty bitmap support is yet to arrive in QEMU). Take backup of the guest XML: $ virsh dumpxml f20vm > /var/tmp/f20vm.xml Undefine the running guest, thus turning it to a transient guest: $ virsh undefine f20vm
(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
Since the a chain was already created in step (3), I should have used '--reuse-external' flag at this shallow blockcopy.
(5) Then live shallow commit of B:
$ virsh blockcommit \ --domain f20vm vda \ --wait --verbose --shallow \ --pivot --active --finish Block Commit: [100 %] Successfully pivoted
-- /kashyap