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.

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 47) 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 R2/2012

•Node Majority

•Node and File Share Majority

NOTE: HP 3PAR Cluster Extension does not support quorum configuration which includes disk witness.

Node Majority quorum in Windows Clustering

The Node Majority resource ensures that the cluster's configuration data is stored locally on the nodes and that it is kept consistent across the different disks. This allows cluster topologies where the nodes do not need shared access to a quorum disk.

(Number of nodes in the cluster/2) +1

12 HP 3PAR Cluster Extension features