Planing for Implementing SAP Solutions on Azure (part 5 of 5)

By Ashwin Venugopal -

 



To read part 1 please click here
To read part 2 please click here
To read part 3 please click here
To read part 4 please click here




SQL Server 2014 Buffer Pool Extension

It introduced a new feature which is called Buffer Pool Extension whose functionality extends the buffer pool of SQL Server, which is kept in memory with a second-level cache that is backed by local SSDs of a server or VM. If we compare Buffer Pool Extension to Azure Premium Storage Read Cache, no significant advantages are expected for Buffer Pool Extensions, as recommended for (SQL Server data files) because both caches are using the local disks of the Azure compute node.

SQL Server Buffer Pool Extension's experiences with SAP workloads is mixed an does not give any clear recommendation on whether to use it on all cases. Hence, its usage is limited to some rare cases and should not be a mainstream case.

Oracle

According the SAP installation manual, Oracle-related files shouldn't be installed or located on system drive hosting the OS instead Oracle Databases and redo log files should be installed on separate data disks except for the Oracle temporary table-space. Single-instance Oracle using NTFS formatted disk is supported only and it is recommended by Microsoft to use Azure Managed Disks with Premium SSDs storage for your Oracle Database deployments. Network drives or remote shares such as Azure file services aren't supported for Oracle Database files.

Vertical & Horizontal Scaling

SAP application servers and the Central Services Clusters can scale up/down or out by simply adding more instances, however, the AnyDB database can scale up/down but does not scale out whose SAP database container does not support sharding. 

SAP HANA Scale-out

The basic configuration of a SUSE Linux VM node for SAP HANA scale-out have following characteristics:

  • For /hana/shared, you build out a highly available NFS cluster based on SUSE Linux 12 SP3 which hosts the /hana/shared NFS share(s) of your scale-out configuration as well as NetWeaver or BW/4HANA Central Services.
  • All the other disk volumes are not shared among the different nodes and are not based on NFS. 

SAP also provides a formula for the size of /hana/shared volume for scale-out as the multiple of the memory size of a single worker node for each four worker nodes and if you take the SAP HANA scale-out certified M128s Azure VM with about 2 TB memory, the recommendations can be as follows:

  • 2 TB size of the /hana/shared volume for up to four worker nodes
  • 4 TB size of the /hana/shared volume for between five and eight worker nodes
  • 6 TB size of the /hana/shared volume for between nine and eleven worker nodes
  • 8 TB size of the /hana/shared volume for between twelve and fifteen worker nodes

Azure does not provide the ability to enforce quality of service and quotas on specific vNICs which results in the separation of client/application facing, and intra-node communication does not offer a mechanism to prioritize one traffic stream over the other. The following points can be considered to optimize the network performance:

  • Since traffic to /hana/shared is moderate, you can route it through the vNIC that is assigned to the client network in the minimum configuration.  
  • Eventually, for the traffic to /hana/shared, you can create a third subnet in the Vnet hosting the SAP HANA scale-out configuration and assign a third vNIC that is hosted in that subnet. After that you can apply separate access and routing rules.

If you want to share the highly available NFS cluster between SAP HANA configurations, you can move all of them into the same VNet.




To read part 1 please click here
To read part 2 please click here
To read part 3 please click here
To read part 4 please click here







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