HP UX Serviceguard Storage Management Software manual Connectivity Policy of Shared Disk Groups

Cluster File System Architecture

About Veritas Cluster Volume Manager Functionality

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

Table 2-3	Allowed and conflicting activation modes
	Disk group	Attempt to activate disk group on another node as:
	activated in	exclusive-	readonly	sharedread	sharedwrite
	cluster as:
		write
	exclusivewrite	Fails	Fails	Succeeds	Fails
	readonly	Fails	Succeeds	Succeeds	Fails
	sharedread	Succeeds	Succeeds	Succeeds	Succeeds
	sharedwrite	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 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.
NOTE	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 vxdg list diskgroup
	command.
	You can also use the vxdg command to change the activation mode on a shared disk
	group.

Connectivity Policy of Shared Disk Groups

The nodes in a cluster must always agree on the status of a disk. In particular, if one node cannot write to a given disk, all nodes must stop accessing that disk before the results of the write operation are returned to the caller. Therefore, if a node cannot

24 Chapter 2