Symantec logo
Activation modes of shared disk groups

A shared disk group must be activated on a node for the volumes in the disk group to become accessible for I/O from that node. The ability of applications to read from or to write to volumes is determined by the activation mode of a shared disk group. Valid activation modes for a shared disk group are exclusive-write, read-only, shared-read, shared-write, and off (inactive). Activation modes are described in the table Activation modes for shared disk groups.


  Note   The default activation mode for shared disk groups is shared-write.


Applications such as high availability and off-host backup can use disk group activation to explicitly control volume access from different nodes in the cluster.

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.

Activation modes for shared disk groups

Activation mode

Description

exclusive-write (ew) 

The node has exclusive write access to the disk group. No other node can activate the disk group for write access. 

read-only (ro) 

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. 

shared-read (sr) 

The node has read access to the disk group. The node has no write access to the disk group, however other nodes can obtain write access. 

shared-write (sw) 

The node has write access to the disk group. 

off 

The node has neither read nor write access to the disk group. Query operations on the disk group are permitted. 

The following table summarizes allowed and conflicting activation modes or shared disk groups:

Allowed and conflicting activation modes

Disk group activated in cluster as...

Attempt to activate disk group on another node as...

exclusive- write

read-only

shared-read

shared-write

exclusive-write

Fails 

Fails 

Succeeds 

Fails 

read-only

Fails 

Succeeds 

Succeeds 

Fails 

shared-read

Succeeds 

Succeeds 

Succeeds 

Succeeds 

shared-write

Fails 

Fails 

Succeeds 

Succeeds 

Shared disk groups can be automatically activated in any mode during disk group creation or during manual or auto-import. To control auto-activation of shared disk groups, the defaults file /etc/default/vxdg must be created.

The defaults file /etc/default/vxdg must contain the following lines:

enable_activation=true

default_activation_mode=activation-mode

The activation-mode is one of exclusive-write, read-only, shared-read, shared-write, or off.


  Caution   When enabling activation using the defaults file, it is advisable that the defaults file be identical on all nodes in the cluster. Otherwise, the results of activation are unpredictable.


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.

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.


  Caution   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.