There were still bugs. You just learned how to deal with them or work around them.

Sorry for the late reply. Using ZFS and replicating the VM first makes it really quick. Less than 5 minutes of downtime.

I did the same a few months ago and was extremely nervous. I have a 4 node cluster running 30 VMs in production. After migrating the VMS off of one node I quickly realized what a pleasure it was to do it. No muss no fuss. Migrated the VMs back and continued on with the other 3.