Unable to set SAP Note 1680803 recommendations for NRREQ using saptune

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

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.