While checking out SAP books or articles, you might have come across below statement related to instance number:
"The instance number is a two-digit number in the range of 00 to 99. If you plan to set up a disaster-tolerant SAP HANA system by using the system replication technology, be aware that such a system will internally need two consecutive instance numbers”
It says that for replication scenario, we need two consecutive instance numbers. But why?
To understand this, first let's have a look at the ports that are used for replication scenario.
Standard Nameserver ports
3<NN>01 - Internal port of the nameserver
Replication specific Nameserver ports
From above port rules, we could observe that single containers use NX as instance number +1 and MDC ports are defined like 4NNxx where NN is instance number itself.
How these rules got derived?
For Single container system, the default replication_port_offset is 100. So, if we add 100 to standard port ex. 30201, then replication port becomes 30301. That's the reason why it says instance number+1
And for MDC systems, the default replication_port_offset is 10000. So, if we add 10000 to standard port ex. 30201, then replication port becomes 40201. That's the reason why we don't have requirement of instance number+1. This approach helps to have more number of instances as N+1 is not reserved.
Can we set this replication_port_offset parameter manually?
Yes we can set it in global.ini. Replication needs to be setup again after changing the parameter.
We'll cover all replication related ports in our further blog.