Active/Active vs Active/Passive clustering

Active/Active vs Active/Passive clusteringNormally I talk in terms of Multi-instance or single instance 2 node clusters. I find that more people use the terms Active/Active and Active/Passive to detail what the cluster is actually doing (rather than single instance multi-instance).

For what people mostly call Active/Active clusters is really a mutli-instance (in terms of SQL Server) cluster with each node owning a running instance with resources leading to both nodes Actively running business logic. In this scenario I mostly see each node owning an instance and having both nodes as possible owners so that if something should happen failover can occur.

For what people mostly call Active/Passive clusters I normally find a single instance of SQL Server (although I have come across a few cases of multi-instance) that runs on one node Actively and the other node does nothing but sit and wait for a failover to occur (passive node). In the few cases I have come across there was more than one instance running on the same node with the other node passively waiting for a failover to occur.

I find that people use these terms interchangeably although they really aren't, however I found this to be in most cases what people are referring to when they talk about active/active or active/passive. Once you get past 2 nodes in the cluster I've heard people say active/active/passive, etc, etc to designate which nodes were actively running business logic. I'm sure there is a better way to describe the scenarios however I find this to be what most use.

Instance= SQL Software installations(Binary)

When you install SQL for the 1st time it is called as Default Instance. When you install SQL again on the same Server (that is 2nd time) it is named instance.

Every instance will have its own services (SQL Database Server and SQL Server Agent one per instance)

CLUSTER ACTIVE/ACTIVE
Important:SQL Server clustering is designed to solve the problem of high availability, not the problem of load balancing.

In SQL Server, Active/Active clustering simply means having two separate instances running in the cluster—one (or more) per machine. So, Active/Active clustering refers to a two-node cluster, with each node running SQL Server instances but each with a different set of databases. This setup is conceptually the same as having two Active/Passive nodes, except that one node must be a named instance.

Example:
Install 1st Node with "Default Instance" then Install 2nd node wih "Named instance"
Default instance will have 2 databases and Named instance will have 2 or 3 differenr databases.

When application or user wants to acess SQL Database they will use virtual SQL Server Name(Virtual IP) and then connect either to Default instance or Named instance based on which database they want to access.

Disadvantages of running multiple Instances on one Sever
1.It takes more processing power and Memory
2.Complex Administration for DBA's

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