Oracle supports out-of-place upgrades, only, because Oracle Clusterware 12c must have its own, new Grid home. For Oracle Clusterware 12c, Oracle supports in-place or out-of-place patching. Oracle supports patch bundles and one-off patches for in-place patching but only supports patch sets and major point releases for out-of-place upgrades.
In-place patching replaces the Oracle Clusterware software with the newer version in the same Grid home. Out-of-place upgrade has both versions of the same software present on the nodes at the same time, in different Grid homes, but only one version is active.
Rolling upgrades avoid downtime and ensure continuous availability of Oracle Clusterware while the software is upgraded to the new version. When you upgrade to Oracle Clusterware 12c, Oracle Clusterware and Oracle ASM binaries are installed as a single binary called the Oracle Grid Infrastructure. You can upgrade Oracle Clusterware in a rolling manner from Oracle Clusterware 10g and Oracle Clusterware 11g, however you can only upgrade Oracle ASM in a rolling manner from Oracle Database 11g release 1 (11.1).
Oracle supports force upgrades in cases where some nodes of the cluster are down.
See Also:
Your platform-specific Oracle Grid Infrastructure Installation Guide for procedures on upgrading Oracle Clusterware