SAP NetWeaver on SQL Server 2012 AlwaysON for HA and DR

[mamartins]

Scenario:

Main Data center + DR

3 physical servers for SQL Server (2 on main DC + 1 DR) AlwaysON

SAP Application Servers hosted under a VMWARE cluster

SAP Netweaver 7.40 SR 2 ABAP, media list:

51047515        SQL Server 2012

51048524_1    NW 7.4 SR2 Installation Export

51048524_2    NW 7.4 SR2 Upgrade Export 1/2

51048524_3    NW 7.4 SR2 Upgrade Export 2/2

51048524_4    NW 7.4 SR2 Language 1/2

51048524_5    NW 7.4 SR2 Language 2/2

51049350_10  SAP Kernel 7.42 Windows Server on x64 64bit

51045590       NW AS ABAP for Suite/NW 7.4 - Enhancement Packages

Software minimum requisites are:

Windows 2008R2

SQL Server 2012

Also, a valid Active Directory Domain is mandatory because the Failover Cluster resources and the SAP distributed AS.

Server names:

SRVDB1 (SQL Server node 1 - main DC)

SRVDB2 (SQL Server node 2 - main DC)

SRVDB3 (SQL Server node 3 - DR)

SRVSAS1 (Central Instance)

SRVSAS2 (Primary Application Server)

SRVSAS3 (Additional Application Server installed on DR)

Relevant SAP notes:

http://service.sap.com/sap/support/notes/965908

http://service.sap.com/sap/support/notes/1365796

http://service.sap.com/sap/support/notes/1772688

The SAP High Availability is done inside the main DC using the HA features of the VMWARE cluster. Also the VM hosting the CI will be replicated to the DR site where another VMWARE cluster is running.

After OS installed and Failover Cluster nodes configured, install SQL Server.  On the main DC, the 2 SQL Server nodes can be pure AlwaysON AG or a FCI. On the first case you have independent storage; on the second one the storage is shared. The replication to the DR will be done with an Availability Group (AG). Microsoft support both scenarios: pure AlwaysON AG or a mix of FCI and AG. The differences between them are:

https://msdn.microsoft.com/en-us/library/ff929171.aspx?f=255&MSPPError=-2147217396

	Nodes within an FCI	Replicas within an availability group
Uses WSFC cluster	Yes	Yes
Protection level	Instance	Database
Storage type	Shared	Non-shared1
Storage solutions	Direct attached, SAN, mount points, SMB	Depends on node type
Readable secondaries	No2	Yes
Applicable failover policy settings	WSFC quorum FCI-specific Availability group settings3	WSFC quorum Availability group settings
Failed-over resources	Server, instance, and database	Database only

1 While the replicas in an availability group do not share storage, a replica that is hosted by an FCI uses a shared storage solution as required by that FCI. The storage solution is shared only by nodes within the FCI and not between replicas of the availability group.

2 Whereas synchronous secondary replicas in an availability group are always running on their respective SQL Server instances, secondary nodes in an FCI actually have not started their respective SQL Server instances and are therefore not readable. In an FCI, a secondary node starts its SQL Server instance only when the resource group ownership is transferred to it during an FCI failover. However, on the active FCI node, when an FCI-hosted database belongs to an availability group, if the local availability replica is running as a readable secondary replica, the database is readable.

3 Failover policy settings for the availability group apply to all replicas, whether it is hosted in a standalone instance or an FCI instance.

Using SWPM, the CI is installed on the appropriate VM. No connection to DB is needed at this time. Once finished, the SAPMNT share will be visible as \\SRVSAS1\SAPMNT.

Then we should logon on the first SQL Server node and start SWPM to install the DB. On this step, the SWPM will only load the SAP DB (tables, views, SP, jobs) and will not create any extra folders or files. The SWPM will need the path to the SAPMNT share to read and update the DEFAULT profile. After the process is completed, the profile will point to the SQL Server node 1 physical name.

After the DB is created, then the AG can be created and the SAP DB replicated. After the listener created, the profile need to be adjusted accordingly (please see the SAP notes posted here). To help create the AG, please check this link: http://www.brentozar.com/archive/2011/07/how-set-up-sql-server-denali-availability-groups/

The next process is the PAS installation and additional AS if needed. The AS installed on DR will be part of the logon group, but will be parametrized to have very low capabilities ensuring that will not be used on normal conditions.

In case of main DC failure, the VM with the CI is booted on the DR site, the IP address is changed and the DNS record reconfigured.

SCN relevant discussions:

http://scn.sap.com/thread/3676897