A VxFS file system mounted with the mount -o cluster option is a cluster, or shared mount, as opposed to a non-shared or local mount. A file system mounted in shared mode must be on a VxVM shared volume in a cluster environment. A local mount cannot be remounted in shared mode and a shared mount cannot be remounted in local mode when you use the mount -o remount option. A single clustered file system can be mounted with different read/writes options on different nodes. These are called asymmetric mounts.
When a primary mounts "ro", this means that neither this node nor any other node is allowed to write the file system. Secondaries can only mount "ro", if the primary mounts "ro". Otherwise, the primary mounts either "rw" or "ro,crw", and the secondaries have the same choice.
Figure: Primary and secondary mounts describes the first column showing the mode in which the primary is mounted: