A shared disk group must be activated on a node in order for the volumes in the disk group to become accessible for application I/O from that node. The ability of applications to read from or to write to volumes is dictated by the activation mode of a shared disk group. Valid activation modes for a shared disk group are exclusivewrite, readonly, sharedread, sharedwrite, and off (inactive).
The default activation mode for shared disk groups is sharedwrite.
Special uses of clusters, such as high availability (HA) applications and off-host backup, can use disk group activation to explicitly control volume access from different nodes in the cluster
Table: Activation modes for shared disk groups describes the activation modes.
Table: Activation modes for shared disk groups
Table: Allowed and conflicting activation modes summarizes the allowed and conflicting activation modes for shared disk groups.
Table: Allowed and conflicting activation modes
To place activation modes under user control, create a defaults file /etc/default/vxdg containing the following lines:
enable_activation=true default_actv_mode=activation-mode
The activation-mode is one of exclusivewrite, readonly, sharedread, sharedwrite, or off.
When a shared disk group is created or imported, it is activated in the specified mode. When a node joins the cluster, all shared disk groups accessible from the node are activated in the specified mode.
The activation mode of a disk group controls volume I/O from different nodes in the cluster. It is not possible to activate a disk group on a given node if it is activated in a conflicting mode on another node in the cluster. When enabling activation using the defaults file, it is recommended that the file be consistent on all nodes in the cluster as in Table: Allowed and conflicting activation modes. Otherwise, the results of activation are unpredictable.
If the defaults file is edited while the vxconfigd daemon is already running, run the /sbin/vxconfigd -k -x syslog command on all nodes to restart the process.
If the default activation mode is anything other than off, an activation following a cluster join, or a disk group creation or import can fail if another node in the cluster has activated the disk group in a conflicting mode.
To display the activation mode for a shared disk group, use the vxdg list diskgroup command.
You can also use the vxdg command to change the activation mode on a shared disk group.
It is also possible to configure a volume so that it can only be opened by a single node in a cluster.