Chapter 5. Compatibility Level Versions

Each host connected to Red Hat Enterprise Virtualization Manager contains a version of VDSM. VDSM is the agent within the virtualization infrastructure that runs on a hypervisor or host and provides local management for virtual machines, networks and storage. Red Hat Enterprise Virtualization Manager controls hypervisors and hosts using current or older versions of VDSM.
The Manager migrates virtual machines from host to host within a cluster. This means the Manager excludes certain features from a current version of VDSM until all hosts within a cluster have the same VDSM version, or more recent, installed.
The API represents this concept as a compatibility level for each host, corresponding to the version of VDSM installed. A version element contains major and minor attributes, which describe the compatibility level.
When an administrator upgrades all hosts within a cluster to a certain level, the version level appears under a supported_versions element. This indicates the cluster's version is now updatable to that level. Once the administrator updates all clusters within a data center to a given level, the data center is updatable to that level.

Example 5.1. Upgrading compatibility levels

The API reports the following compatibility levels for Red Hat Enterprise Virtualization Manager 2.2 instance:
<host ...>
    ...
    <version major="2" minor="2"/>
    ...
</host>

<cluster ...>
    ...
    <version major="2" minor="2"/>
    <supported_versions/>
    ...
</cluster>

<data_center ...>
    ...
    <version major="2" minor="2"/>
    <supported_versions/>
    ...
</data_center>
All hosts within a cluster are updated to VDSM 3.0 and the API reports:
<host ...>
    ...
    <version major="3" minor="0"/>
    ...
</host>

<cluster ...>
    ...
    <version major="2" minor="2"/>
    <supported_versions>
        <version major="3" minor="0"/>
    </supported_versions>
    ...
</cluster>

<data_center ...>
    ...
    <version major="2" minor="2"/>
    <supported_versions/>
    ...
</data_center>
The cluster is now updatable to 3.0. When the cluster is updated, the API reports:
<cluster ...>
    ...
    <version major="3" minor="0"/>
    <supported_versions/>
    ...
</cluster>

<data_center ...>
    ...
    <version major="2" minor="2"/>
    <supported_versions>
        <version major="3" minor="0"/>
    </supported_versions>
    ...
</data_center>
The API user updates the data center to 3.0. Once upgraded, the API exposes features available in Red Hat Enterprise Virtualization 3.0 for this data center.