HP 3PAR Cluster Extension Software Administrator Guide for Windows (5697-1821, April 2012)

Synchronous replication
Using synchronous mode, all write requests from the server are first transferred to the remote storage
system. After each I/O has been mirrored in the cache area of the remote storage system, it is
acknowledged to the local storage system. The write request is then acknowledged to the server.
Asynchronous Periodic Replication
In the asynchronous periodic mode, host writes are performed only on the primary server and the
host write is acknowledged as soon as the data is written into cache on the primary storage server.
User configuration file
HP 3PAR Cluster Extension provides a user configuration file to customize failover behavior. You
can specify all customizable objects of HP 3PAR Cluster Extension in this file.
See “User configuration file” (page 63) for more information.
Force Flag
The force flag forces HP 3PAR Cluster Extension to skip the internal logic and enables write access
to the local virtual volumes regardless of the Remote Copy volume group member state. You can
set this flag when you are sure that the current site contains the latest data, even though a previous
application service startup process failed because HP 3PAR Cluster Extension discovered a Remote
Copy volume group member state that could not be handled automatically.
To use the force flag feature, before starting the application service that uses HP 3PAR Cluster
Extension, you must create a file called application_name.forceflag in the directory specified
by the ApplicationDir property. While using clx3PARrun to use the force flag feature, use the
operand –forceflag to eliminate the need of creating the application_name.forceflag file
. The application_name.forceflag is the name of the HP 3PAR Cluster Extension resource.
Before creating this file, ensure that the application service is not running elsewhere. This file is
removed after it is detected by HP 3PAR Cluster Extension.
You cannot use the force flag if the local virtual volume state is a combination of secondary and
syncing, which indicates that a copy operation is in progress. A disk cannot be put in read/write
access mode when a write operation is in progress to that virtual volume; in this case, HP 3PAR
Cluster Extension returns a global error.
Planning for HP 3PAR Cluster Extension
Consider the dependencies described in this section before configuring HP 3PAR Cluster Extension.
Cluster setup considerations
Windows clustering
Windows Clustering depends on a quorum resource to maintain a persistent log of cluster
configuration changes and status, as well as a single point to resolve any possible events that
could result in a split-brain situation. HP 3PAR Cluster Extension supports the following quorum
configurations in which one site failure will not cause the entire cluster to fail.
Windows Server 2008/2008 R2
• Node Majority
• Node and File Share Majority
Windows Server 2003
• Majority Node Set (MNS)
• Majority Node Set with File Share Witness
14 HP 3PAR Cluster Extension features