Database
If the database server is not available, the entire SAP system is inoperative. For this reason special attention should be paid to providing the ability to keep the database server available. Availability of the database server can be thought of in two degrees, high availability and continuous availability. High availability provides for the ability to reduce the impact of an unplanned outage such as a database server abend. Continuous availability provides for the ability to reduce the impact of both planned and unplanned outages.
It is recommended that you use SA z/OS® for automating the starting, stopping, monitoring, and restarting of the database server. With SA z/OS you are able to achieve high availability for the non-data-sharing configuration and continuous availability for the data sharing configuration.
The following sections discuss the impact of database server unavailability when running in non-data-sharing and data-sharing configurations.
Non-data sharing
In a non-data-sharing configuration, the database server is a single point of failure. Whenever it is unavailable, the entire SAP system is inoperative. There are two reasons why the database server might not be available: planned and unplanned outages.
Be aware that the Db2 utilities like RUNSTATS, REORG, or BACKUP SYSTEM are designed to work in an online fashion. Therefore, the SAP and Db2 systems can remain up and running while you run utilities. Also, a large number of Db2 system parameters (ZPARMs) can be changed while the Db2 system remains up and running.
In this configuration, the database server must be stopped whenever there is a need to upgrade or apply maintenance to it or to z/OS. Such downtimes are generally referred to as planned outages and are unavoidable but can be scheduled at a convenient time.
For unplanned outages of the database server, there are several tools, for example z/OS Automatic Restart Manager, that can be utilized to minimize their impact by quickly restarting the database server.
SA z/OS provides the added advantage of automating daily operational activities such as starting, stopping, and monitoring the entire SAP system, including the database server. SA z/OS also ensures that components are started and stopped in the proper sequence. The automating of these activities provides for quicker SAP system start-ups with less errors, thus providing improved overall system availability.
Data sharing
A data sharing configuration eliminates the database server as a single point of failure and provides for near continuous availability. In a data sharing configuration, planned outages can be avoided by using Db2 connection failover (see Db2 connection failover) to move the workload off the Db2 member needing the outage to an available Db2 member in the data sharing group. In the case of an unplanned outage, Db2 connection failover is used to switch the workload to a surviving Db2 member. In either situation, the SAP system remains available to the end users.
In a data sharing configuration, system automation becomes even more important because there are more database server components to deal with. As previously stated, automating the daily operations of starting, stopping, and monitoring all the components of the SAP system provides for improved SAP system availability by eliminating most human errors.
For a more detailed description of the SAP profile parameters that influence failover support, refer to the Database Administration Guide for SAP on IBM® Db2 for z/OS, section Sysplex Failover and Connection Profile.