Recommended SUSE SLES 4 SAP Settings

This document (7024082) is provided subject to the disclaimer at the end of this document.

Environment

SUSE Linux Enterprise Server 12 for SAP Applications
SUSE Linux Enterprise Server 15 for SAP Applications SP1

Situation

There are five OS Settings known to Support that have the potential to change or influence the OS behaviour in a SAP Environment. They are covered in different SAP Notes which might lead to some of them being missed.

1) the I/O Scheduler

The I/O Scheduler is responsible for the I/O Delivery to the back-end.

The Default on SUSE Linux Enterprise Server 12 and SUSE Linux Enterprise Server 15 SP1 is cfq.

For most SAP environments (e.g. RAID, storage arrays, virtualization) the IO scheduler 'noop' (non-multiqueue) or 'none' (multiqueue) is the better choice.

To set the scheduler, the recommendation is to use sapconf or saptune.
Recent versions of sapconf and saptune support both schedulers by default and will set either "noop" or "none" as default.

Please test the impact of the available schedulers and choose the most effective one.

This is also mentioned in SAP Notes 1984787 1680803 2161991

More information can also be found:
https://documentation.suse.com/sles/15-SP2/html/SLES-all/cha-tuning-io.html

2) dirty_bytes

The Dirty Bytes are a Threshold Setting. It comes in different Flavours, as a Ratio or Direct Byte Value. Once this defined Threshold is reached, the Kernel will write out all the Dirty Bytes in one go.

As this is the Kernel itself the System might appear to hang.

It is recommended to set the Dirty Bytes, and to set them low, for example to

vm.dirty_background_bytes = 314572800

vm.dirty_bytes = 629145600

beginning on any Machine with more than 8GB of Memory.

This is mentioned in SAP Note 1984787.

3) transparent_hugepages

The Transparent Hugepages should always be disabled. Either as Kernel Command line

transparent_hugepage=never

or online without Reboot

echo never >/sys/kernel/mm/transparent_hugepage/enabled

This is mentioned in SAP Note 2205917.

4) cstate

The Sleep States of the Processor will not help in a SAP Environment and should be disabled as Kernel Commandline

intel_idle.max_cstate=1 processor.max_cstate=1

This is mentioned in SAP Note 2205917.

5) pagecache_limit_mb

The pagecache_limit_mb is a special enhancement from SUSE and will limit the Pagecache.

This is only supported on SLES 4 SAP.

This setting can be beneficial, but has to be set to the right value, or should be turned off. So it has either be set it to the correct value, which can be found in SAP Note 1557506 - Linux paging improvements, or set to 0.

Resolution

To set these Values it is recommended to use saptune. If sapconf is installed it should be removed first. As an added benefit, all other SAP recommended Settings will be applied by saptune.

saptune is installed via zypper :

zypper in saptune

It should be ensured that the version being installed is >= 2.0.1

benromach:~ # rpm -q saptune
saptune-2.0.1-8.16.1.x86_64

It could be checked for a complete solution, for this example HANA is used

benromach:~ # saptune solution list
All solutions (* denotes enabled solution, O denotes override file exists for solution, D denotes deprecated solutions):
        BOBJ               - 941735 1771258 1984787 SAP_BOBJ
        HANA               - 941735 1771258 1980196 1984787 2205917 2382421 2534844
D      MAXDB              - 941735 1771258 1984787
        NETWEAVER          - 941735 1771258 1984787
        NETWEAVER+HANA     - 941735 1771258 1980196 1984787 2205917 2382421 2534844
        S4HANA-APP+DB      - 941735 1771258 1980196 1984787 2205917 2382421 2534844
        S4HANA-APPSERVER   - 941735 1771258 1984787
        S4HANA-DBSERVER    - 941735 1771258 1980196 1984787 2205917 2382421 2534844
        SAP-ASE            - 941735 1410736 1680803 1771258 1984787

To set, for example, pagecache_limit_mb the note 1557506 would be customized :

benromach:~ # saptune note customise 1557506

To pick the I/O Scheduler to be used the note 1984787 could be customized :

benromach:~ # saptune note customise 1984787

Then the whole solution can be applied in one go as well :

benromach:~ # saptune solution apply HANA
    WARNING: [block] section detected: Traversing all block devices can take a considerable amount of time.
    WARNING: Be aware: system-wide UserTasksMax is now set to infinity according to SAP recommendations.
This opens up entire system to fork-bomb style attacks.
    WARNING: System does not support Intel's performance bias setting
    WARNING: governor settings not supported by the system
    WARNING: latency settings not supported by the system
All tuning options for the SAP solution have been applied successfully.

it can be checked at a later time what tuning is applied with a simple command :

benromach:~ # saptune note list

current order of applied notes is: 941735 1771258 1980196 1984787 2205917 2382421 2534844

to add the pagecache_limit_mb a single note can be applied with the command :

benromach:/ # saptune note apply 1557506

Cause

Clarification on the correct use of SUSE SLES 4 SAP recommended settings

Disclaimer

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