4.0.0 HP PolyServe Software for Microsoft SQL Server Administration Guide (T5392-96056, March 2010)

The following configuration also has one node providing a backup for the Virtual SQL Servers on
other nodes. In this example, the SQL instances associated with the Virtual SQL Servers all have the
same name, “instance1.”
This configuration supports only one failover at a time. If the Virtual SQL Server on node 1 (“virtual1”)
fails over and node 2 then goes down, the Virtual SQL Server on node 2 (“virtual2”) will not be able
to fail over. This occurs because “instance1” on node 4 is currently providing access to the databases
for the “instance1” associated with the Virtual SQL Server “virtual1.”
A similar situation occurs when a Virtual SQL Server is moved to maintenance mode (for example, to
apply a service pack). In maintenance mode, all SQL instances associated with the Virtual SQL Server
are shut down on the primary and backup nodes. In the above example, if the Virtual SQL Server on
node 1 (“virtual1”) is moved to maintenance mode, “instance1” on node 1 and also its backup
“instance1” on node 4 will be shut down. There is now no backup available for “instance1” on node
2 and node 3. To minimize the time without a backup, HP recommends that you perform the
maintenance on the backup instance first and then reenable it. The backup instance will then be
available for the other primary instances.
SQL monitors and failover
When you add a SQL instance to a Virtual SQL Server, HP PolyServe Software creates a service
monitor for that instance. The monitor is active on the node currently hosting the Virtual SQL Server
and periodically determines whether the SQL service is up.
If the monitor detects that the SQL service is down, HP PolyServe Software can attempt to restart the
service. (When you create the monitor, you can specify the number of times that HP PolyServe Software
should try to restart the service.) If the attempts are not successful, by default the Virtual SQL Server
will fail over to a backup node.
You can customize the failover behavior for each SQL service monitor. For example, you can use the
Policy configuration option to specify whether the Virtual SQL Server should fail back to the original
node or remain on the backup node after the problem causing the failover has been corrected.
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:
HP PolyServe Software for Microsoft SQL Server administration guide 11