Enqueue Replication Server HA

[Former Member]

Dear friends, we are planning an HA instalation, but we have a doubt about the Enqueue Replication Server. As per my understanding, we can install en enqueue replication server (ERS) in other host (B), but in case of fail over, the sap instance needs to be started in the same host of the ERS (B) to be able to access to the lock table of the ERS.

Do you know if posible to instal the ERS in other host, and the sap instance in another? The scenario looks like:

Before Fail Over:

Host A: ASCS + CI.

Host B: Stand by Server for the failover.

Host C: ERS.

After Fail over:

Host A: Stand by Server for the failover.

Host B: ASCS + CI.

Host C: ERS.

Will be possible for the host B read the replicated lock table in the host C after the fail over?

The documentation says that the replicated lock table is stored in a shared memory area, then, when the instance is started in the other host (failover) is cappable to read this information form the shared memory area. But what happens if the ERS is in a separated host?

Thanks and best regards.

Hector.

[Former Member · Accepted solution]

Hi Hector,

The Basic of High availability is to distribute SAP Single point of Failures to nodes which can fail over.

For SAP, the SPOFs are Enqueue and Database. in High availability installation, the server is divided into ASCS which has Enqueue if installing on Unix(ERS is separate in Windows cluster configuration), DB, CI and Dialog instance.

so ASCS and DB should be on separate nodes which can fail over.

With the config you gave above, what if your host C goes down, your system will collapse.

Its better to keep ERS in ASCS and distribute DB and ASCS on separate nodes.

AC