Unable to set SAP Note 1680803 recommendations for NRREQ using saptune

This document (000020344) is provided subject to the disclaimer at the end of this document.

Environment

SUSE Linux Enterprise Server for SAP 15 SP3 on KVM or Azure
SUSE Linux Enterprise Server for SAP 15 SP2 on KVM or Azure

Situation

Problem: Unable to set /sys/block/sda/queue/nr_requests using saptune to the recommended value of 1024 by SAP Note 1680803 on SUSE Linux Enterprise Server for SAP 15 SP2 (on Azure or KVM).

This works correctly for SUSE Linux Enterprise Server for SAP 15 SP1.

The none scheduler does not allow for the value for the disk to be set to 1024 if the detected hardware does not support such a value (which on virtualised hardware may well be the case):

sles15sp2sap:/etc/saptune # saptune note verify 1680803
    WARNING: [block] section detected: Traversing all block devices can take a considerable amount of time.
    INFO: Trying scheduler in this order: noop, none.
    INFO: 'none' will be used as new scheduler for device 'sda sdb sdc'.

1680803 - Sybase - SAP Adaptive Server Enterprise            Version 24 from 20.11.2017

SAPNote, Ver| Parameter        | Expected | Override| Actual | Compliant
------------+------------------+----------+---------+--------+-----------
...
1680803, 24 | IO_SCHEDULER_sda | none     |         | none   | yes
1680803, 24 | IO_SCHEDULER_sdb | none     |         | none   | yes
1680803, 24 | IO_SCHEDULER_sdc | none     |         | none   | yes
1680803, 24 | NRREQ_sda        | 1024     |         | 332    | no
1680803, 24 | NRREQ_sdb        | 1024     |         | 332    | no 
1680803, 24 | NRREQ_sdc        | 1024     |         | 332    | no  

...

echo 1024 > /sys/block/sda/queue/nr_requests
-bash: echo: write error: Invalid argument

 

Resolution

Run the following command

 

saptune note customise 1680803

 

to delete everything (it is a copy of the Note) that is not needed, then change the value to the maximum detected value for the hardware:

[block]
NRREQ=


After saving, the file /etc/saptune/override/1680803 exists. Alternatively, this file can be created manually.

The Note must be reapplied for the changes to take effect:

sles15sp2sap:/etc/saptune # saptune note verify 1680803
    WARNING: [block] section detected: Traversing all block devices can take a considerable amount of time.
    INFO: Trying scheduler in this order: noop, none.
    INFO: 'none' will be used as new scheduler for device 'sda sdb sdc'.

1680803 - Sybase - SAP Adaptive Server Enterprise      Version 24 from 20.11.2017

SAPNote, Ver| Parameter        | Expected | Override| Actual | Compliant
------------+------------------+----------+---------+--------+-----------
...
1680803, 24 | IO_SCHEDULER_sda | none     |         | none   | yes
1680803, 24 | IO_SCHEDULER_sdb | none     |         | none   | yes
1680803, 24 | IO_SCHEDULER_sdc | none     |         | none   | yes
1680803, 24 | NRREQ_sda        | 332      |untouched| 332    | yes
1680803, 24 | NRREQ_sdb        | 332      |untouched| 332    | yes  
1680803, 24 | NRREQ_sdc        | 332      |untouched| 332    | yes 
...


The override has been used and therefore the parameter is SAP Note compliant.

Cause

What changed?
SUSE Linux Enterprise Server for SAP 15 SP1 used noop as a scheduler.
SUSE Linux Enterprise Server for SAP 15 SP2 uses none, as noop is no longer supported.

The none scheduler enforces the max NRREQ value for the hardware detected.

The SAP Note needs to be modified in order to reflect this.

Disclaimer

This Support Knowledgebase provides a valuable tool for SUSE customers and parties interested in our products and solutions to acquire information, ideas and learn from one another. Materials are provided for informational, personal or non-commercial use within your organization and are presented "AS IS" WITHOUT WARRANTY OF ANY KIND.

  • Document ID:000020344
  • Creation Date: 23-Jul-2021
  • Modified Date:23-Jul-2021
    • SUSE Linux Enterprise Server for SAP Applications

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