As of MS SQL Server 2000 you can install more than one instance on a single computer and to operate each instance separately. In an SAP environment this means that you can, for example, install two SQL Server instances with two corresponding SAP databases. Each SAP database can be managed with its own corresponding SQL Server instance. Each instance operates in isolation of the other allowing administrative tasks to be carried out on one instance without affecting the other instances.
The following graphic illustrates a multiple instance configuration with the two SAP databases <SAPSID1> and <SAPSID2>.
If you want to set up a multi-instance configuration, you must install each SQL Server instance as a named instance that is assigned a unique name. In an SAP environment, this name must be the same as that of the corresponding SAP database. For example, if the SAP database (system) is called C11, the SQL server instance must also be called C11.
The advantage of multiple instances is that you can set up several SAP instances on the same host and administer each one separately. The main components of the SQL Server are exclusively available for each instance, SQL Server resources do not have to be shared and administrative tasks performed on one instance do not interfere with other instances.
In a typical SAP configuration only one SQL Server instance and one SAP database are installed on a single computer. For this configuration, it is recommended that you install a default SQL Server instance. You can specify that you want to install a default instance during the SQL Server installation process.
A default instance is recommended, if you plan to install only one SAP database on a computer. A named instance is recommended, if you plan to install more than one SAP database on the same host.