High Availability: Intel® Optane™ PMem
For SAP HANA running on VMware vSphere, you can implement high availability with Intel® Optane™ persistent memory (PMem).
When running SAP HANA in a VMware vSphere environment, Intel® Optane™ PMem can significantly expand system memory resources. And when combined with the power of virtualization, it can help enterprises lower their total cost of ownership. Intel Optane PMem running in App Direct mode can deliver near-DRAM-level performance and enable far larger SAP HANA in-memory database capacity while simultaneously providing data persistence in the event of unplanned failure. This, in turn, can yield faster restart times and higher uptime because data is already in memory and doesn’t need to be restored from external storage resources.
VMware enabled high-availability (HA) functionality in vSphere 7.0 U2 for Intel Optane PMem-enabled SAP HANA VMs. However, to ensure complete data transfer, additional steps are needed to prepare Intel Optane PMem for SAP HANA use so that it can automatically reload the data from shared (conventional) storage after the failover.
VMware added the HA functionality for Intel Optane PMem and SAP HANA VMs because of the novel way SAP HANA data and Intel Optane PMem interact. VMware vSphere does not support HA for direct-attached storage, such as NVDIMMs or local SSDs. This makes logical sense. How could one automatically fail over a direct-attached storage resource onto a physically separate system? However, when Intel Optane PMem is used in App Direct mode, it appears to vSphere as a direct-attached memory device; that matters because application data kept in Intel Optane PMem on the failed system needs to be brought up on the new system running SAP HANA.
To illustrate, consider a four-node cluster where Hosts 1, 2, and 4 have Intel Optane PMem and Host 3 does not. If Host 1 running an SAP HANA VM using Intel Optane PMem fails, vSphere HA failover will restart the VM on either Host 2 or 4 (depending on the load if VMware’s Dynamic Resource Scheduler is enabled). But because PMem appears as direct-attached storage, the data will not migrate across hosts and thus will not be available on the PMem on Hosts 2 or 4. vSphere HA will start a new PMem (NVDIMM) device on the restored VM, and SAP HANA will only be able to reload the PMem data if the same device mappings and permissions are also restored.
With vSphere 7.0 U2, to allow a virtualized SAP HANA PMem system to start automatically after an HA event, the OS direct-access type (DAX) device configuration required by SAP HANA must be re-created. There is no single exact way to implement the script to set up the OS to configure SAP HANA with Intel Optane PMem on vSphere. Rather, there are three key elements that need to be implemented:
- Creating the PMem file system.
- Defining the file system’s mount points.
- Assigning SAP HANA with the right permissions to the file system.
This technology brief provides sample scripts to help you accomplish these three steps.