Bias - Adjustment factor
In the context of z/OS and JES2 (Job Entry Subsystem 2), a bias is a numerical weighting factor applied to a resource, such as an initiator or an output device, to influence its selection by JES2. It acts as an adjustment to the resource's perceived availability or priority, making it more or less likely to be chosen for job execution or output processing.
Key Characteristics
-
- Numerical Weight: Expressed as an integer value, typically ranging from 0 to 255, where higher values generally indicate a stronger preference for selection.
- Resource Specific: Applied to individual JES2 initiators (e.g.,
INIT(n)), output devices (printers, punches), or groups of these resources. - Influences Selection Algorithm: JES2's internal algorithms use bias values, along with other factors like job class and device characteristics, to determine which available resource is most suitable.
- Dynamic Adjustment: Bias values can be changed dynamically using JES2 operator commands (e.g.,
$T INIT(n),BIAS=value) without requiring a JES2 restart. - Not a Hard Constraint: A bias is a preference, not a strict rule. A resource with a low bias can still be selected if no other suitable resources are available.
- Part of Workload Management: Used to fine-tune resource allocation and balance workloads across multiple systems or devices within a JES2 multi-access spool (MAS) complex.
Use Cases
-
- Prioritizing Initiators: Assigning a higher bias to initiators on a specific LPAR or with access to particular datasets (e.g., for critical applications) to ensure their preferential use.
- Workload Balancing: Distributing jobs evenly across a pool of similar initiators or printers by adjusting their biases to prevent bottlenecks on any single resource.
- Printer Selection: Directing high-volume, sensitive, or special-form printing to specific printers by giving them a higher bias, while general output goes to others.
- Resource Decommissioning: Gradually phasing out an initiator or printer by setting its bias to 0 (or a very low value) to reduce its workload before taking it offline.
- Testing and Maintenance: Temporarily lowering the bias of a resource to reduce its assigned workload during testing of new configurations or scheduled maintenance.
Related Concepts
Bias is a crucial element in JES2's resource selection process, working in conjunction with job classes, initiator groups, and device groups. While job classes define which jobs can run on which initiators, bias refines *which* available initiator is chosen based on a preference. It complements JES2 job priority and execution priority by providing an additional layer of control, influencing overall throughput and turnaround time within the z/OS environment. It helps JES2 optimize the utilization of shared resources in a MAS complex.
- Document Bias Settings: Maintain clear and current documentation of why specific bias values are assigned to resources to aid in troubleshooting and future adjustments.
- Monitor and Adjust: Regularly monitor initiator and device utilization (e.g., using
$D INITor$D PRTcommands) after making bias changes to ensure the desired workload distribution is achieved. - Gradual Changes: Implement small, incremental changes to bias values and observe the impact before making larger adjustments to avoid unintended consequences.
- Avoid Over-Biasing: Do not excessively bias a single resource, as this can lead to bottlenecks and underutilization of other perfectly capable resources.
- Consider Automation: For complex or highly dynamic environments, explore using automation tools or scripts to dynamically adjust bias values based on real-time workload metrics or system health.