Upgrading vSphere objects and applying patches or extensions with Update Manager is a multistage process in which procedures must be performed in a particular order. Following the suggested process helps ensure a smooth update with a minimum of system downtime.
The Update Manager process begins by downloading information (metadata) about a set of patches, extensions, and virtual appliance upgrades. One or more of these patches or extensions are aggregated to form a baseline. You can add multiple baselines to a baseline group. A baseline group is a composite object that consists of a set of nonconflicting baselines. You can use baseline groups to combine different types of baselines, and scan and remediate an inventory object against all of them as a whole. If a baseline group contains both upgrade and patch or extension baselines, the upgrade runs first.
A collection of virtual machines, virtual appliances, and ESX/ESXi hosts or individual inventory objects can be scanned for compliance with a baseline or a baseline group and later remediated. You can initiate these processes manually or through scheduled tasks.