Veritas Storage Foundation 5.0.1 Cluster File System Administrator's Guide Extracts for the HP Serviceguard Storage Management Suite on HP-UX 11i v3

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 contact a disk, it should contact
another node to check on the disk’s status. If the disk fails, no node can access it and the nodes
can agree to detach the disk. If the disk does not fail, but rather the access paths from some of
the nodes fail, the nodes cannot agree on the status of the disk. Either of the following policies
for resolving this type of discrepancy may be applied:
• Under the global connectivity policy, the detach occurs cluster-wide (globally) if any node
in the cluster reports a disk failure. This is the default policy.
• Under the local connectivity policy, in the event of disks failing, the failures are confined to
the particular nodes that saw the failure. However, this policy is not highly available because
it fails the node even if one of the mirrors is available. Note that an attempt is made to
communicate with all nodes in the cluster to ascertain the disks’ usability. If all nodes report
a problem with the disk, a cluster-wide detach occurs.
Limitations of Shared Disk Groups
The cluster functionality of VxVM does not support RAID-5 volumes, or task monitoring for
cluster-shareable disk groups. These features can, however, be used in private disk groups that
are attached to specific nodes of a cluster. Online relayout is supported provided that it does not
involve RAID-5 volumes.
The root disk group cannot be made cluster-shareable. It must be private.
Only raw device access may be performed via the cluster functionality of VxVM. It does not
support shared access to file systems in shared volumes unless the appropriate software, such
as the HP Serviceguard Storage Management Suite, is installed and configured.
If a shared disk group contains unsupported objects, deport it and then re-import the disk group
as private on one of the cluster nodes. Reorganize the volumes into layouts that are supported
for shared disk groups, and then deport and re-import the disk group as shared.
22 Cluster File System Architecture