3.4.3 MxDB for SQL Server Installation and Administration Guide

Chapter 1: Introduction 5

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). MxDB for SQL Server

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.

• Starts SQL Server and SQL Agent on the backup node and updates

registry keys.

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

MxDB for SQL Server 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.