I think that coupling the engine upgrade with the new slaves is not necessary. we can start by installing the hook on ovirt-srv11 and spinning up new slaves, that way we can also test the hook in production. because there is no NFS involved, and live migration isn't working with the hook, the host is pretty much self-contained and this can't harm anything.
FYI. We used to have fc21-scratchpad-test slave running in u/s ovirt in production for certainly more than half a year for sure. Not sure why it was delete and was it related to local disk or not. But I think this should be enough to consider it has being tested in production. What was not tested is the effect on NFS server as we had only one slave. But nowadays seeing overrun counters on storages we can conclude that it will help since anything directing traffic away from the storages will help. Anton. -- Anton Marchukov Senior Software Engineer - RHEV CI - Red Hat