SAP HANA provides mechanism for business continuity and disaster recovery for system faults and software errors. High availability in HANA system defines set of practices that helps to achieve business continuity in case of disaster like power failures in data centers, natural disasters like fire, flood, etc. or any hardware failures.
SAP HANA high availability provides fault tolerance and ability of system to resume system operations after an outage with minimum business loss.
The following illustration shows the phases of high availability in HANA system −
First phase is being prepared for the fault. A fault can be detected automatically or by an administrative action. Data is backed up and stand by systems take over the operations. A recovery process is put in action includes repair of faulty system and original system to be restored to previous configuration.
To achieve high availability in HANA system, key is the inclusion of extra components, which are not necessary to function and use in case of failure of other components. It includes hardware redundancy, network redundancy and data center redundancy. SAP HANA provides several levels of hardware and software redundancies as below −
HANA System Hardware Redundancy
SAP HANA appliance vendors offer multiple layers of redundant hardware, software and network components, such as redundant power supplies and fans, error-correcting memories, fully redundant network switches and routers, and uninterrupted power supply (UPS). Disk storage system guarantees writing even in the presence of power failure and use striping and mirroring features to provide redundancy for automatic recovery from disk failures.
SAP HANA Software Redundancy
SAP HANA is based on SUSE Linux Enterprise 11 for SAP and includes security pre-configurations.
SAP HANA system software includes a watchdog function, which automatically restarts configured services (index server, name server, and so on), in case of detected stoppage (killed or crashed).
SAP HANA Persistence Redundancy
SAP HANA provides persistence of transaction logs, savepoints and snapshots to support system restart and recovery from failures, with minimal delay and without loss of data.
HANA System Standby and Failover
SAP HANA system involves separate standby hosts that are used for failover, in case of failure of the primary system. This improves the availability of HANA system by reducing the recovery time from an outage.