ABCs of z/OS System Programming Volume 3 - IBM Redbooks

SMB processing techniques
If all of the required conditions are met, SMB is invoked when option SYSTEM or an SMB
processing technique is used in the fields described previously. SMB is disabled when USER
is entered instead (USER is the default). Since JCL information takes precedence over data
class information, installations can enable or disable SMB for some executions.
The information contained in SMB processing techniques is needed because SMB must
maintain an adequate algorithm for managing the CIs in the resource pool. SMB accepts the
ACB MACRF options when the I/O operation is requested. For this reason, the installation
must accurately specify the processing type, through ACCBIAS options:
► Direct Optimized (DO)
SMB optimizes for totally random record access. When this technique is used, VSAM
changes the buffering management from NSR to LSR.
► Direct Weighted (DW)
The majority is direct access to records, with some sequential.
► Sequential Optimized (SO)
Totally sequential access.
► Sequential Weighted (SW)
The majority is sequential access, with some direct access to records.
When SYSTEM is used in JCL or in the data class, SMB chooses the processing technique
based on the MACRF parameter of the ACB.
For more information about the use of SMB, refer to VSAM Demystified, SG24-6105.
180 ABCs of z/OS System Programming Volume 3