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
The default activation mode for shared disk groups is
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
Activation modes for shared disk groups describes the activation modes.
The node has read access to the disk group and denies write access for all other nodes in the cluster. The node has no write access to the disk group. Attempts to activate a disk group for either of the write modes on other nodes fail.
Allowed and conflicting activation modes summarizes the allowed and conflicting activation modes for shared disk groups.
To place activation modes under user control, create a defaults file
/etc/default/vxdg containing the following lines:
The activation-mode is one of
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 this file be made identical on all nodes in the cluster. Otherwise, the results of activation are unpredictable.
If the defaults file is edited while the
vxconfigd daemon is already running, the
vxconfigd process must be restarted for the changes in the defaults file to take effect.
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
list diskgroup command.
See "Listing shared disk groups" on page 424.
You can also use the
vxdg command to change the activation mode on a shared disk group.
See "Changing the activation mode on a shared disk group" on page 428.
It is also possible to configure a volume so that it can only be opened by a single node in a cluster.
See "Creating volumes with exclusive open access by a node" on page 429.
See "Setting exclusive open access to a volume by a node" on page 429.