A Veritas File System (VxFS) file system mounted with the mount -o cluster option is a cluster, or a shared mount, as opposed to a non-shared or a 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/write options on different nodes. These are called asymmetric mounts.
Asymmetric mounts allow shared file systems to be mounted with different read/write capabilities. For example, one node in the cluster can mount read-write, while other nodes mount read-only.
When a primary mounts "ro", this means that neither this node nor any other node is allowed to write to 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.
You can specify the cluster read-write (crw) option when you first mount the file system, or the options can be altered when doing a remount (mount -o remount).
Figure: Primary and secondary mounts shows the different modes in which the primary node and secondary nodes can be mounted:
The check marks indicate the mode secondary mounts can use for a given mode of the primary.
Mounting the primary with only the -o cluster,ro option prevents the secondaries from mounting in a different mode; that is, read-write.