4.1.0 HP PolyServe Software for Microsoft SQL Server administration guide (T5392-96074, October 2010)

What happens during a failover?
Failovers can be planned (for example, upgrading the operating system) or unplanned
(such as a crash of a primary node). HP PolyServe Software takes these actions
during a failover:
• Removes the IP address for the Virtual SQL Server from the original node and
then adds it to the backup node.
• Updates registry keys and then starts SQL Server and SQL Agent on the backup
node.
Clients using the IP address of the Virtual SQL Server will now access the databases
on the PSFS filesystem via the SQL instance on the backup node.
After a Virtual SQL Server fails over, by default it remains on the backup node.
(Optionally, you can configure the Virtual SQL Server to automatically fail back to
the original node.)
Replication of registry keys
HP PolyServe Software replicates the registry keys for the SQL server from the local
machine to a location on the PSFS filesystem containing the corresponding “master”
SQL databases. The replicator watches the main SQL instance key and, if it changes,
persists the key to the shared filesystem.
If a Virtual SQL Server fails over to a backup node, that node reads the keys from
the PSFS filesystem and applies them back before starting SQL services. On failback,
after SQL services are stopped on the backup node, the registry is returned to its
original state on that node.
Virtual SSAS
HP PolyServe Software includes high availability support for Microsoft SQL Server
2005/2008 Analysis Services (SSAS) instances, which provide online analytical
processing (OLAP) and data mining features. A Virtual SSAS is configured on at least
two cluster nodes, with one node serving as the primary and the other nodes as
backups. SSAS instances are then associated with the Virtual SSAS. The SSAS
instances are accessed via the Virtual SSAS. If a problem occurs on the primary
node, the Virtual SSAS can fail over to a backup node, which will then provide access
to the SSAS instances. See Chapter 6 on page 99, for more information about
configuring SSAS for high availability.
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