Special requirements apply to configuring the persistence (data and log) of an SAP HANA VM.

Dell EMC recommends using Linux Logical Volume Manager (LVM) devices for the SAP HANA persistence. LVM enables a striping of the logical volumes across multiple vSAN devices to provide better performance and flexible administration. LVM also enables resizing of logical volumes if capacity adjustments are required.

The following sections provide step-by-step instructions for configuring the SAP HANA persistence on Linux LVM devices.

Configure the SCSI controller

A VMware best practice is to use a dedicated SCSI controller for the SAP HANA persistence. Configure the SCSI controller as VMware Paravirtual. The example in the following figure uses SCSI Controller 0 for the system device, SCSI Controller 1 for the LVM data devices, and SCSI Controller 2 for the LVM log devices:

Figure 5.   VM SCSI controller for the SAP HANA persistence

Configure the device capacity on the SAP HANA persistence

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 VM. For data, configure 2 x RAM. For log, configure 0.5-1 x RAM (up to a maximum of 512 GB).

Add the capacity of the data and the log device to get the total required capacity for the SAP HANA persistence of the VM.

Assign VM storage policies to the SAP HANA persistence

You must define a storage policy for the SAP HANA LVM physical devices that are deployed on the vSAN datastore. While the default vSAN storage policy is adequate for the system device, a dedicated storage policy is required for the SAP HANA persistence devices to meet the SAP performance requirements. The following figures show the rules that we defined in the storage policy:

Figure 6.   VM storage policy: Availability for the SAP HANA persistence

Figure 7.   VM storage policy: Advanced policy rules for the SAP HANA persistence

Storage policy requirements for the SAP HANA persistence

The vSAN storage policy requirements for the SAP HANA persistence are:

• Failure tolerance method = RAID 1 (mirroring)
  RAID 1 provides best performance on vSAN compared to RAID 5/6, which is mainly optimized for space utilization.
• Failures to tolerate = 1
  This setting indicates the number of disk, host, or fault-domain failures that a storage object can tolerate.

• Number of disk stripes per object = 12
  This setting indicates the number of disks across which each replica of a storage object is striped (with RAID 1, each storage object has two replicas). The optimal number depends on the number of available disk groups and capacity disks. The minimum, which is also the default, is 1, and the maximum is 12.
• Object space reservation = Thick provisioning
  This setting specifies the type of device provisioning.
• Flash read cache reservation (%) = 0
  This setting applies to hybrid vSAN deployments. Only all-flash deployments of vSAN Ready Nodes for SAP HANA are certified and supported.
• Disable object checksum = Off
  During read/write operations, vSAN checks for data validity based on the checksum. If data is not valid, vSAN either corrects the data by retrieving a new copy from another replica or reports it to the user to take action (nonrecoverable errors).
• Force provisioning = Off
  If this option is turned on, the object is provisioned even if the policy specified in the storage policy is not satisfiable with the resources that are currently available in the cluster.

Assign vSAN devices for the SAP HANA persistence to the VM and use the devices in LVM

Linux LVM distributes the logical volumes that are used by the application across multiple physical devices—in this case, vSAN devices. Distribute the persistence for the data device across eight physical devices and the persistence for the log device across four physical devices.

In the following example, we needed 500 GB capacity for the SAP HANA data device and 200 GB for the SAP HANA log device—a total of 700 GB for the persistence. Thus, we created eight 62 GB vSAN devices for data and four 52 GB devices for log.

Every volume uses the VM storage policy SAP_HANA and is assigned to the dedicated SCSI controller, as shown in the following figure:

Figure 8.   Assigning a VM storage policy SAP_HANA and SCSI controller to each disk

Add devices to Linux LVM and create the SAP HANA persistence

After adding devices to the VM, follow these steps in Linux to partition the devices and add them to LVM:

1. Rescan the SCSI devices by running the following Linux command:

rescan-scsi-bus.sh

2. Verify that the devices are visible by running the fdisk –l command.
3. Create a Linux LVM partition on each device.

The best way to do this is to create a text file (for example, fdin.txt) with the following content:

n
p
1


t
8e
w

4. Create a partition on a device by running a command such as:

cat fdin.txt | fdisk /dev/sdb

This command creates new LVM partitions on the devices; dev/sdb1 is an example. These partitions can be used as physical devices in LVM.

5. Repeat the preceding command for every device that you create for the SAP HANA persistence.
6. Add the devices as physical devices to LVM:

pvcreate /dev/sdb1 /dev/sdc1 /dev/sdd1 /dev/sde1 /dev/sdf1 /dev/sdg1 /dev/sdh1 /dev/sdi1 /dev/sdj1 /dev/sdk1 /dev/sdl1 /dev/sdm1

7. Create an LVM volume group with the name hana-data for data:

vgcreate hana-data /dev/sdb1 /dev/sdc1 /dev/sdd1 /dev/sde1 /dev/sdf1 /dev/sdg1 /dev/sdh1 /dev/sdi1

8. Create a second LVM volume group with the name hana-log for log:

vgcreate hana-log /dev/sdj1 /dev/sdk1 /dev/sdl1 /dev/sdm1

9. Create logical volumes for the SAP HANA data and log file systems on the new volume groups by running the lvcreate command. For example:

lvcreate --name data --size 500G --stripes 8 --stripesize 64 hana-data

and

lvcreate --name log --size 200G --stripes 4 --stripesize 64 hana-log

Note: Use the number of physical devices you created earlier as the --stripes parameter.

10. Format the devices by running the following command:

mkfs.xfs /dev/mapper/hana—data-data and mkfs.xfs /dev/mapper/hana—log-log

11. Mount the formatted devices under the required mount points for SAP HANA. For example:

mount /dev/mapper/hana-data /hana/data

and

mount /dev/mapper/hana-log /hana/log

12. To persist the mounts over reboots, add the corresponding entries to /etc/fstab.