IBM Spectrum Scale Sharing Nothing Cluster performance tuning guide has been posted and please refer to link before you doing the below change.

If the cluster is focused on database workloads such as SAP HANA/DB2 DPF/DashDB or DIO/AIO, the following configuration options must be tuned:

Database workload customers using direct I/O must also enable the following preStealPct tuning if they are running any of the following Spectrum Scale levels: 3.5 (any PTF level), 4.1.1 (below PTF 10), 4.2.0 (any PTF level), or 4.2.1 (below PTF 2). These database workload customers with direct I/O enabled running these older code levels must tune preStealPct as follows:
echo 999 | mmchconfig preStealPct=0 -i

After upgrading to IBM Spectrum Scale from one of the previously referenced older code levels to a higher level, especially (4.1.1 PTF 10, 4.2.1 PTF 2, or 4.2.2.0 or higher, you can set the configuration option ‘preStealPct=0’ back to its default value as follows:
echo 999 | mmchconfig preStealPct=1 -i

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