SAP HANA High Availability Setup
What is High Availability? Availability is usually indicated as a percentage of the operational uptime of a system, measured over the course of a year. For example, if a system is designed to be available 99.99% of the time (sometimes called “four nines”), its downtime per year must be less than 0.01%, or 52 minutes and 56 seconds. That means less than an hour of downtime per year. This can be a very challenging target. To meet such challenging targets, high availability and disaster tolerance should be an integral part of the architectural design, that is, implemented on every layer of the infrastructure.
Downtime is the consequence of outages, which may be planned downtime (such as that for system upgrades or hardware replacements) or caused by unplanned downtime (such as that for software or hardware failures). Unplanned downtime can be triggered by equipment malfunction, software, or network failures, or a major disaster such as a fire, earthquake, a regional power loss, or a construction accident which may decommission the entire data center.
High Availability is a set of techniques, engineering practices, and design principles for business continuity. This is achieved by eliminating single points of failure (fault tolerance), and providing the ability to rapidly resume operations after a system outage with minimal business loss (fault resilience).
Fault Recovery is the process of recovering and resuming normal operations after an outage due to a fault.
Disaster Recovery is the process of recovering operations after an outage due to a prolonged data center or site failure. Preparing for disasters may require backing up data across longer distances and may thus be more complex and costly. Recovery – Key Performance Indicators (KPIs) Customers commonly use two key measures to specify the recovery parameters of a system following an outage: The Recovery Period Objective (RPO) and the Recovery Time Objective (RTO). The RPO and RTO of a system are illustrated in the following figure.