A highly available application or system is the key concept in cluster environment. Microsoft SQL Server is a cluster-aware application, and it works well to cater for this business need. Let's see how it works.
Before we go further into details, let's see some common terms here:
Active/Passive Cluster: In this setup, there will be one server that remains idle and takes over the control or the ownership of the resources at the time of failover.
Active/Active Cluster: Here, the only difference is that both the nodes in the cluster are active and running, and the surviving node will take over the control or the ownership of the resources when a failover occurs.
Public Network: This is a network available to external resources or systems.
Private Network aka Heartbeat: This is a network that is available to SQL Server cluster nodes only; heartbeat is used to check the health of another node.
Shared Disk Array: A disk array is nothing but more than one disk used collectively and shared among the cluster nodes. However, at any point of time only one node — the active node or the owner of the resources — can access the disks, in order to protect data from being overwritten.
Quorum: This is the disk resource wherein the status of the cluster is being written, especially by the Windows clustering. Failure of this resource can lead to failure of the entire clustering setup.
Cluster IP: This refers to the IP address on the public network that is used by external systems or client machines to connect to the cluster.
Cluster Resource Type: This can be any resource that can be configured for clustering, that is, a physical disk.
Cluster Account: This is the Administrator account used to control and run the services for a cluster; this account must be configured at the domain level and should be added to the local administrator group in each cluster node.
Cluster Group: This is a kind of container, for example, SQL Server, wherein cluster-aware applications or services are grouped.
Cluster Name for Virtual SQL Server: This is the name of a Virtual SQL Server, which is then used by client machines to connect to.
IP for Virtual SQL Server: This will be the IP address used by SQL Server, and clients use this IP address to connect to SQL Server.