In this article I will discuss about the resources that are part of a SQL Server failover cluster.
A SQL Server failover cluster instance consists of 2 kinds of resources.
1)Local Resources: Local resources are those components that are installed on each possible owner node. They remain on that node and do not move over during a failover.
2)The shared resources: Those resources that fail over between the owner nodes.
Let us now go through the resources that are part of a resource group in a SQL Server failover cluster.
a) SQL Server Database Engine\Agent service : The database engine and SQL Server agent resources are always part of any SQL Server failover cluster’s resource group where the database engine has been installed. If SQL server analysis service is installed, then it will be a part of the resource group. From an availability and performance perspective it is better if both are installed on separate resource groups.
b) IP Address and Network name: The IP address and network name component ensures an interface that clients can use to connect to the SQL Server instance irrespective of the fact that which node is currently serving the cluster. During a failover event, the network name and IP addresses is registered to redirect to the new node that is serving the SQL Server failover cluster instance. To the clients that are connecting to the SQL Server, this is a absolutely transparent process.
c) Shared disks:A SQL Server shared disk contains all of the system and user data including databases, logs for the SQL Server failover cluster instance. When a failover occurs, the disks are mounted on the new node. When SQL Server instance is started on the new node, it goes through recovery as part of the SQL Server startup and maintains access to the same database files that existed when it was running on the previous node.The shared disks are the single point of failure for a failover cluster instance. Windows Server and SQL Server failover clustering provides redundancy for machines, operating systems, and SQL Server binaries, but requires reliable storage to assure availability of the shared storage.