Special requirements apply when you configure the SAP HANA persistence (data and log) of an SAP HANA virtual machine.
Dell EMC strongly recommends using Linux Logical Volume Manager (LVM) devices for the SAP HANA persistence. LVM allows striping of the logical volumes across multiple vSAN devices, which provides flexible administration and better performance. LVM also allows resizing of logical volumes if capacity must be adjusted.
The following sections provide step-by-step instructions for configuring the SAP HANA persistence on Linux LVM devices.
A VMware best practice is to use a dedicated SCSI controller for the SAP HANA devices. Configure the SCSI controller as VMware Paravirtual. The example in the following figure uses SCSI Controller 0 for the system device and SCSI Controller 1 for the LVM devices.
Figure 5. VM SCSI controller for the SAP HANA persistence
In addition, set the following Linux kernel settings in the virtual machine:
In a SUSE Linux virtual machine, you can set these parameters by using yast2 and the System Bootloader settings for the kernel parameters. For more information, see the VMware Knowledge Base article KB2053145: Large-scale workloads with intensive I/O patterns might require queue depths significantly greater than Paravirtual SCSI default values.
Use the SAP Quick Sizer tool to determine the required capacity for the SAP HANA data and log devices. If the sizing details are not available, Dell EMC recommends configuring the sizes of the data and log devices based on the memory size of the SAP HANA virtual machine: for data, configure 2x RAM; for log, configure 0.5-1x RAM. For more information, go to the Quick Sizer website.
Add the capacity of the data and the log devices to get the total capacity required for the SAP HANA persistence of the virtual machine.
The SAP HANA LVM physical devices deployed on the vSAN datastore must have a storage policy assigned. While the default vSAN storage policy is adequate for the system device, the SAP HANA persistence devices must have a dedicated storage policy to meet the SAP performance requirements. The following figure shows the rules in the storage policy for the SAP HANA persistence:
Figure 6. VM storage policy for the SAP HANA persistence
The vSAN storage policy requirements can be summarized as follows:
Dell EMC engineers performed the VxRail HCI certification tests with four capacity disks per disk group. They found that setting 12 disk stripes per object provided the best overall results.
Linux LVM distributes the logical volumes used by the application across multiple physical devices―in our case, vSAN devices. Dell EMC recommends distributing the persistence across four to eight physical devices (four is the minimum number while eight is the maximum). In our example below, we need 500 GB capacity for the SAP HANA data device and 200 GB for the SAP HANA log device. Therefore, a total of 700 GB is required for the SAP HANA persistence. We created eight 100 GB vSAN devices to allow some free space in case additional capacity is required later.
Figure 7. vSAN devices for the HANA persistence
Every 100 GB volume uses the VM storage policy “HANA-Persistence” and is assigned to the dedicated SCSI controller 1, as shown in the following figure:
Figure 8. Assign VM storage policy and SCSI controller
SAP HANA persistent devices can be thin-provisioned because the storage policy has the Object space reservation (%) = 100 setting, which means that the device is thick-provisioned by default.
After the devices have been added to the VM, follow these steps in Linux to partition the devices and add them to LVM:
This command creates new LVM partitions on the devices, for example, /dev/sdb1, which can be used as physical devices in LVM. Repeat this command for every device created for the SAP HANA persistence.