In some scenarios it becomes necessary to perform maintenance in such a way that still leaves a virtual workload on a host. I use the term “live host maintenance” to describe a host that is not in maintenance mode but is not yet ready for active, priority workloads. One example would be to test various feature of the host, such as a load or network test. In this situation, you are unable to use maintenance mode on the host but still do not wish to have any other workloads on the host, especially if you are working on an issue. This is where your good friend Migration Threshold priority 1 comes in handy.
The process is straight forward:
1. Set the cluster’s vSphere DRS level to Fully Automated and Migration Threshold to priority 1.
2. Select the host you wish to do work on and enter maintenance mode to force all of the VMs off. This is a shortcut to let the cluster balance the workloads over the rest of the hosts.
3. Once finished, exit maintenance mode on that host.
4. Migrate a test VM onto the host and perform your tests.
5. When satisfied, revert the vSphere DRS level back to the original state. For my lab, that’s Migration Threshold priority 3 (default).
