Veritas Storage Foundation 5.0 Cluster File System Administration Guide Extracts for HP Serviceguard Storage Management Suite, Second Edition, May 2008

Cluster File System Architecture
About Veritas Cluster Volume Manager Functionality
Chapter 2
24
The following table summarizes the allowed and conflicting activation modes for shared
disk groups:
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
Table 2-3 Allowed and conflicting activation modes
Disk group
activated in
cluster as:
Attempt to activate disk group on another node as:
exclusive-
write
readonly sharedread sharedwrite
exclusivewrite Fails Fails Succeeds Fails
readonly Fails Succeeds Succeeds Fails
sharedread Succeeds Succeeds Succeeds Succeeds
sharedwrite Fails Fails Succeeds Succeeds