Live Migrate VM with Local Storage: virsh migrate
In my previous post I lamented that it seemed I could not migrate a VM between virtual hosts without shared storage. This is incorrect. I have just completed a test run based on an old mailing list message:
ServerA> virsh -c qemu:///system list Id Name State ---------------------------------------------------- 5 testvm0 running ServerA> virsh -c qemu+ssh://ServerB list # Test connection to ServerB Id Name State ----------------------------------------------------
The real trick is to work around a bug whereby the target disk needs to be created. So, on ServerB, I created an empty 8G disk image:
ServerB> sudo dd if=/dev/zero of=/var/lib/libvirt/images/testvm0.img bs=1 count=0 seek=8G
Or, if you’re into backticks and remote pipes:
ServerB> sudo dd if=/dev/zero of=/var/lib/libvirt/images/testvm0.img bs=1 count=0 seek=`ssh ServerA ls -l /var/lib/libvirt/images/testvm0.img | awk '{print $5}'`
Now, we can cook with propane:
ServerA> virsh -c qemu:///system migrate --live --copy-storage-all --persistent --undefinesource testvm0 qemu+ssh://ServerB/system
This will take some time. I used virt-manager to attach to testvm0’s console and ran a ping test. At the end of the procedure, virt-manager lost console. I reconnected via ServerB and found that the VM hadn’t missed a ping.
And now:
ServerA> virsh -c qemu+ssh://ServerB/system list Id Name State ---------------------------------------------------- 4 testvm0 running
Admittedly, the need to manually create the target disk is a little more janky than I’d like, but this is definitely a nice proof of concept and another nail in the coffin of NAS being a hard dependency for VM infrastructure. Any day you can kiss expensive, proprietary SPOF dependencies goodbye is a good day.
