Sep 6, 2012

SAP instance


SAP instance resides on an Application Server under the directory: 

Windows: x:\usr\sap\sapsid 
Unix/Linux: /usr/sap/sapsid 

The SAP instance on an Application Server communicates with a database associated with this instance. 

SAP instance on an Application Server together with its associated database is called an "SAP System". 

The term "SAP System" is also known as "SAP Installation". 

When you talk about an SAP System or an SAP Installation, you are talking about an SAPSID folder on an Application Server and the database associated with this folder.
Multiple SAP Instances
One Application Server (or host) could contain multiple SAP instances. 

In other words there would be multiple SAPSID folders under the directory /usr/sap (x:\user\sap on Window). 

Where SAPSID is the actual name of the SAP identifier; for example: PROD, TEST etc. 

Each SAPSID folder would point to its own database. 

SAP System refers to the pair of SAP instance and its database. 

The folder /usr/sap could contain more than one SAP instance. 

It is important to know the difference between SAP System (pairing) and SAP instance (folder).
Load Balancing
When number of users increases, load balancing is implemented. 

The SAPSID folder is simply cloned to more than one Application Servers. 

Load is shared by making users connect to different Application Servers. 

Load balancing software controls which user would connect to would Application Server. 

SAPSID folders on all Application Servers would be talking to the same database. 

All sibling SAPSID folders together with their database would be called one SAP System. 

When load balancing is implemented, SAP System would consist of multiple SAPSID folders on difference Application Server machines and a database. 

An Application Server may host more than one SAP instance under the directory /usr/sap

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