SAP HANA System Replication - RTO & RPO

In our last blog, we saw what actually is high availability in context of SAP. If you haven't checked it out yet, you can go through this link.

In this blog, we will specifically talk about Hana System replication concept.

What is System Replication?

As we checked, it's a way to achieve high availability in case of outage due to planned maintenance, faults and disasters. It has a very low RTO of few minutes and a RPO of 0 seconds.

RTO - Recovery Time Objective is the time taken to make the secondary/standby system available after the failure of primary system.

RPO - Recovery Point Objective is the difference between the timestamp at which the primary system failed and the timestamp of the latest replicated logs/data available on secondary system.

System replication is supported in every hana installation and can be used for HA as well as DR scenarios. 

It is configured as exact copy of the primary system with same number of worker nodes. We can setup multitier system as well by establishing replication between primary to secondary and secondary to dr_site

When secondary site is located near the primary system, we call the deployment scenario as HA which serve as rapid failover. And when the site is far from primary site, we call that scenario as DR.

The instances in a secondary system operate in recovery mode. In this mode each service establishes a connection with its counterpart and requests a snapshot of the data in the primary system. After that point, all logged changes in the primary system are replicated. 
Whenever logs are persisted in the primary system, they are also sent to the secondary system. A transaction in the primary system is not committed until the logs are replicated.

We can configure replication in different types of replication modes. We will cover them in detail in our next blog and will also see what happens in case standby system goes down.