Veritas Volume Manager 5.0.1 Administrator's Guide, HP-UX 11i v3, First Edition, November 2009

group imported (importing host) must deport (give up access to) the disk group.
Once deported, the disk group can be imported by another host.
If two hosts are allowed to access a disk group concurrently without proper
synchronization, such as that provided by the Oracle Parallel Server, the
configuration of the disk group, and possibly the contents of volumes, can be
corrupted. Similar corruption can also occur if a file system or database on a raw
disk partition is accessed concurrently by two hosts, so this problem in not limited
to Veritas Volume Manager.
Import lock
When a host in a non-clustered environment imports a disk group, an import lock
is written on all disks in that disk group. The import lock is cleared when the host
deports the disk group. The presence of the import lock prevents other hosts from
importing the disk group until the importing host has deported the disk group.
Specifically, when a host imports a disk group, the import normally fails if any
disks within the disk group appear to be locked by another host. This allows
automatic re-importing of disk groups after a reboot (autoimporting) and prevents
imports by another host, even while the first host is shut down. If the importing
host is shut down without deporting the disk group, the disk group can only be
imported by another host by clearing the host ID lock first (discussed later).
The import lock contains a host ID (in Veritas Volume Manager, this is the host
name) reference to identify the importing host and enforce the lock. Problems
can therefore arise if two hosts have the same host ID.
Since Veritas Volume Manager uses the host name as the host ID (by default), it
is advisable to change the host name of one machine if another machine shares
its host name. To change the host name, use the vxdctl hostid new_hostname
command.
Failover
The import locking scheme works well in an environment where disk groups are
not normally shifted from one system to another. However, consider a setup where
two hosts, Node A and Node B, can access the drives of a disk group. The disk
group is first imported by Node A, but the administrator wants to access the disk
group from Node B if Node A crashes. Such a failover scenario can be used to
provide manual high availability to data, where the failure of one node does not
prevent access to data. Failover can be combined with a “high availability” monitor
to provide automatic high availability to data: when Node B detects that Node A
has crashed or shut down, Node B imports (fails over) the disk group to provide
access to the volumes.
Administering cluster functionality
Multiple host failover configurations
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