When we talk about high availability, we mostly think it's just the hana system replication.
But, this is not the right statement, especially in case of SAP Hana. To know the reason, let's get into the concept of high availability.
High availability is a method or a set of techniques that allows us achieve business continuity. This basically means that the system should be available continuously to run the business.
SAP HANA is designed in such a way that it properly supports high availability. It can help us prevent our system from faults, software errors & disasters.
Following are the high level concepts that help us achieve high availability in SAP:
- Fault tolerance - It is the ability of a system to suffer a fault but continue to operate. It eliminates single points of failure.
- Fault resilience - It is the ability to recover quickly from an outage
- Fault recovery - It is the process of recovering and resuming operations after an outage due to a fault
- Disaster recovery - It is the process of recovering operations after an outage due to a prolonged data center or site failure
Note: Fault tolerance and high availability augment each other in the field of IT resilience, so you may find different definitions at multiple places. We suggest you not to consider those definitions here.
Defense mechanisms supported by Hana for failure related outages:
- Hardware Redundancy - SAP HANA appliance vendors offer multiple layers of redundant hardware, software and network components, such as redundant power supplies and fans, enterprise grade error-correcting memories, fully redundant network switches and routers, and uninterrupted power supply (UPS). Disk storage systems use batteries to guarantee writing even in the presence of power failure, and use striping and mirroring to provide redundancy for automatic recovery from disk failures. Generally speaking, all these redundancy solutions are transparent to SAP HANA's operation, but they form part of the defense against system outage due to single component failures.
SAP HANA supports the following recovery measures from failures:
In our next blog we'll specifically talk about hana system replication.