Data Rate

Enhanced Definition

In the mainframe context, **Data Rate** refers to the speed at which data is transferred between components, such as between a CPU and storage devices, or over network links. It quantifies the volume of data moved per unit of time, typically measured in bits per second (bps) or bytes per second (Bps). It is a critical metric for evaluating the performance of the z/OS I/O subsystem and network connectivity.

Key Characteristics

- Units of Measurement: Commonly expressed in megabits per second (Mbps), gigabits per second (Gbps) for network interfaces, or megabytes per second (MB/s), gigabytes per second (GB/s) for storage and channel paths.
- I/O Performance Metric: A critical indicator of the efficiency and capacity of the mainframe's I/O subsystem, directly impacting application response times, batch job completion, and overall system throughput.
- Device Dependent: Varies significantly based on the type of hardware component, such as disk drives (DASD), tape drives, network adapters (OSA-Express), and the underlying channel technology (e.g., FICON, ESCON).
- Channel Path Influence: The maximum data rate achievable for I/O operations is often dictated by the speed of the I/O channel path connecting the CPU to the control unit and device.
- Raw vs. Effective Rate: The raw data rate is the theoretical maximum bandwidth of a component, while the effective data rate is the actual sustained throughput, which is often lower due to overheads like protocol processing, error correction, and contention.

Use Cases

- DASD Performance Evaluation: Assessing the data transfer capabilities of storage arrays (e.g., IBM DS8000 series) to ensure they can handle the I/O demands of critical applications like DB2 or IMS databases.
- Network Link Sizing: Determining the required bandwidth for OSA-Express adapters and network infrastructure to support high-volume data transfers for z/OS Connect, MQ, or FTP between the mainframe and distributed systems.
- Tape Drive Throughput: Calculating the speed at which data can be written to or read from tape drives (e.g., TS7700 Virtual Tape Library or physical tape drives) for backups, archives, or disaster recovery operations.
- Channel Path Capacity Planning: Analyzing the data rate of FICON or ESCON channels to identify potential bottlenecks and ensure sufficient bandwidth for I/O-intensive workloads.

Related Concepts

Data Rate is a fundamental aspect of the I/O Subsystem, directly influencing the throughput and latency of operations. It is closely tied to channel path technologies like FICON and OSA-Express, which define the physical speed limits. Performance monitoring tools like RMF (Resource Measurement Facility) and SMF (System Management Facilities) collect metrics related to data rates, helping system programmers identify bottlenecks and optimize resource utilization. A higher data rate generally contributes to better application performance and faster batch job execution.

Best Practices:

Monitor I/O Performance: Regularly use RMF and SMF reports to monitor actual data rates across channels, control units, and devices to identify and address performance degradation.