Tuning for System-Managed Buffering

VSAM can use system-managed buffering (SMB) to determine the number of buffers and the type of buffer management to use for VSAM data sets.

To indicate that VSAM is to use SMB, specify one of the following options:

Specify the ACCBIAS subparameter of the JCL DD statement AMP parameter and an appropriate value for record access bias.
Specify Record Access Bias in the data class and an application processing option in the ACB.

For system-managed buffering (SMB), the data set must use both of the following options:

System Management Subsystem (SMS) storage
Extended format (DSNTYPE=ext in the data class)

JCL takes precedence over the specification in the data class. You must specify NSR. SMB either weights or optimizes buffer handling toward sequential or direct processing.

To optimize your extended format data sets, use the ACCBIAS subparameter of the AMP parameter along with related subparameters SMBVSP, SMBDFR, and SMBHWT. You can also use these subparameters with Record Access Bias=SYSTEM in the data class. These subparameters are only for Direct Optimized processing.