Making changes to VMware pvscsi driver parameters aligned with SAP recommendations

This document (000019614) is provided subject to the disclaimer at the end of this document.

Environment

SUSE Linux Enterprise Server for SAP Applications 12 Service Pack 3
SUSE Linux Enterprise Server for SAP Applications 12 Service Pack 4
SUSE Linux Enterprise Server for SAP Applications 12 Service Pack 5
SUSE Linux Enterprise Server for SAP Applications 15
SUSE Linux Enterprise Server for SAP Applications 15 Service Pack 1
SUSE Linux Enterprise Server for SAP Applications 15 Service Pack 2
SUSE Linux Enterprise Server for SAP Applications 15 Service Pack 3
SUSE Linux Enterprise Server for SAP Applications 15 Service Pack 4

Situation

Best practice tuning recommendations, advise the following changes are made to the standard pvscsi parameters:

vmw_pvscsi.cmd_per_lun=254
vmw_pvscsi.ring_pages=32

but does not explain exactly how to make the changes and if these changes can be made in some dynamic way without the need for a reboot.

Resolution

These changes can not be made dynamically as the pvscsi driver does not allow driver module unload/load/reload, once the virtual machine is active.

The only way to make these changes is to add the parameters to the appropriate grub boot entry and reboot.

Edit /etc/default/grub and change the line GRUB_CMDLINE_LINUX_DEFAULT= e.g.:

GRUB_CMDLINE_LINUX_DEFAULT="resume=/dev/sda2 mitigations=auto splash=silent vmw_pvscsi.cmd_per_lun=254 vmw_pvscsi.ring_pages=32 quiet showopts crashkernel=183M,high crashkernel=72M,low"

Then run: grub2-mkconfig -o /boot/grub2/grub.cfg e.g.:

# grub2-mkconfig -o /boot/grub2/grub.cfg
Generating grub configuration file ...
Found theme: /boot/grub2/themes/SLE/theme.txt
Found linux image: /boot/vmlinuz-<version>-default
Found initrd image: /boot/initrd-<version>-default
done

This will generate a new /boot/grub2/grub.cfg file and the changes made will survive updates to the system which cause the regeneration of grub.cfg

Cause

In order to increase the queue depth of the pvSCSI driver inside the Linux-based guest on which SAP HANA runs, add the Linux kernel boot options below :

vmw_pvscsi.cmd_per_lun=254
vmw_pvscsi.ring_pages=32

Additional Information

These recommendations can be found in several current VMware documents, including:

Architecture Guidelines And Best Practices For Deployments of Sap Hana On VMware vSphere
: Architecture And Technical Considerations Guide

Large-scale workloads with intensive I/O patterns might require queue depths significantly greater than Paravirtual SCSI default values (2053145)

Note: Previously, in older documents from SUSE and VMware, the advice was to set vmw_pvscsi.cmd_per_lun to 1024. However, this advice has been changed by VMware in more recent documents and this TID has been changed to reflect that. Please refer to VMware for questions related to VMware specific settings.

Disclaimer

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