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]

I agree with Alberto here in that the enqueue process needs access to the replicated lock informatin in order to restart cleanly and keep the SAP application locks valid. So yes the ASCS should start on a node where the ERS runs.

RE: Amit's comment perhaps I don't understand it but the ASCS and ERS should be split. If the ERS is maintaining replicated lock information and runs on the same node as the ASCS, and therefore the enqueue process, then if the node goes down both the primary and replicated lock information will be lost which defeats the point of having an ERS in the first place.

There is an option to store lock information at the file system level but this is not recommended due to latency on I/O. Never seen this be used.