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Chapter 6. SAP high availability
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SAP solutions are deployed to support important business functions for companies that
operate 24 hours a day, 7 days a week. Sometimes almost all business processes run on
SAP applications, making it crucial to maximize system availability. Downtime can result in a
loss of revenue or failure to meet customers commitments.
Availability is the amount of time that an application is accessible to the user. It is usually a
percentage. The objective of a high available solution is to be as near to 99.999% (the
5nines) available as possible.
Downtime can occur in two ways:
Planned downtime The result of a maintenance activity that involves a disruption to
system operation. It includes patches installation, or other changes
that take effect only upon a reboot.
Unplanned downtime Unscheduled outages typically as a consequence of a hardware or
software failure.
High availability implies no manual intervention to restore operation. For example, availability
at 99.999% allows about one second of downtime per day, which is impractical using human
labor.
Based on IBM Tivoli® System Automation, with a redesign of the SAP central instance
concept, this high availability solution uses the following features to guarantee a minimum of
system outages and a maximum of automation:
► New SAP stand-alone enqueue server
► The enqueue replication server
► Dynamic virtual IP addresses (VIPAs)
► Shared hierarchical file system (HFS)
► DB2 data sharing
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