The following HA solutions currently support the Enqueue Server 2 according to the statement of the HA partners:
- Fujitsu FlexFrame Orchestrator
- HPE Serviceguard
- IBM PowerHA
- Microsoft Windows Failover Cluster – My Preferred (Wil provide the reason)
- NEC EXPRESSCLUSTER
- Oracle Clusterware (on SAP NetWeaver 7.52 only)
- Oracle Solaris Cluster (on SAP NetWeaver 7.52 only)
- Red Hat Enterprise Linux High Availability Add-On
- SUSE Linux Enterprise Server for SAP Applications
- Veritas Infoscale Availability
According to SAP, the Standalone Enqueue Server 2 (ENSA2) is the successor to the standalone enqueue server. It is a component of the SAP lock concept and manages the lock table. The major difference between the Vendor HA certification for SAP S/4 HANA and SAP NetWeaver is beginning with the version ABAP platform 1809 SAP has changed to the new Enqueue Standalone Architecture (ENSA2).
This principle ensures the consistency of data in an ABAP system. If there is a failover, the old Standalone Enqueue Server was required to “follow” the Enqueue Replication Server. That is, the HA software had to start the ASCS instance on the host where the ERS instance is currently running. In contrast to the old Standalone Enqueue Server, the new Standalone Enqueue Server 2 and Enqueue Replicator 2 no longer have these restrictions.
What’s the primary difference between ENSA1 and ENSA2 here?
Under the mechanism of the old Standalone Enqueue Server (ENSA1), the ASCS has to failover to the cluster node where the active ERS is running, because it has to access the shared memory that stores the enqueue replication table. ENSA1 is supported in pacemaker as a two-node cluster configuration, mainly because of the restriction that ASCS must “follow” ERS.
Standalone Enqueue Server has evolved into generation 2 since Netweaver 7.51, known as Standalone Enqueue Server 2, or ENSA2. In ENSA2, if the ASCS failed, it can start on a separate node in the cluster, and copy the lock entries from the enqueue replicator 2. Just like the old standalone enqueue server, the new Standalone Enqueue Server 2 runs together with the message server on the ABAP central services instance (ASCS instance). The Standalone Enqueue Server 2 prevents multiple users from simultaneously accessing the same data by using the lock table to hold all current user locks in the main memory.
There are different possibilities to get HA system based on Enqueue Server 2:
- Migration of the old Enqueue Server to the Enqueue Server 2 (at least SAP NetWeaver 7.52 necessary)
- Installation of ABAP Platform 1809
- Upgrade to ABAP Platform 1809
ABAP Platform 1809 ==> Starting with ABAP Platform 1809 and 1909 Foundation, it deploy the Standalone Enqueue Server 2 (and Enqueue Replicator 2 for high-availability scenarios) and installed by default. S/4HANA 1809 and BW/4HANA 2.0 and later are based on ABAP Platform 1809 which uses the new Standalone Enqueue Server 2 (ENSA2) by default based on SAP Notes/KBAs.
This release still supports the Standalone Enqueue Server (including replication support using Enqueue Replication Server).
However, we recommend migrating to the Standalone Enqueue Server 2 because future improvements will be implemented only in this version. The upgrade to ABAP Platform 1809 migrates to Standalone Enqueue Server 2 automatically.
Below SAP demonstration for std. HA Cluster Nodes works on Network level for NW solutions for basic understanding of HA functionality especially for newbies.
For more info. on ENSA2 please refer to SAP Note 2630416 – Support for Standalone Enqueue Server 2