834973-B25 HPE 3 Meter Infiniband EDR QSFP Copper Cable

Key Use Cases and Typical Deployments

This cable is frequently chosen for environments where performance and low latency are critical and where distances between devices are short — typically within the same rack or adjacent racks. Common deployment scenarios include:

• High-performance computing (HPC) clusters requiring RDMA and minimal latency for parallel workloads.
• Machine learning training farms and GPU clusters where fast inter-node communication accelerates training time.
• Enterprise and hyperscale data centers optimizing east-west traffic between top-of-rack (ToR) switches and compute nodes.
• Storage networks employing InfiniBand-attached storage appliances or NVMe over Fabrics (NVMe-oF) over InfiniBand.

The HPE 834973-B25 for InfiniBand Connectivity

Selecting the HPE 834973-B25 DAC provides several advantages compared with fiber or longer copper alternatives when the environment allows short-range connections:

• Cost efficiency: Passive copper DACs are typically less expensive than active optical transceivers plus fiber patching for equivalent short distances.
• Power savings: Passive copper cables do not require external power or active electronics at the transceiver, reducing power consumption.
• Plug-and-play simplicity: Direct attach cabling is straightforward to install — no transceiver modules to configure and fewer moving parts.
• Optimized latency: The direct electrical connection reduces serialization and conversion delays, beneficial for latency-sensitive applications.

Technical Specifications and Capabilities

The technical design of the 834973-B25 targets robustness, signal integrity, and compatibility. Below are the primary characteristics and capabilities that make this cable an excellent fit for modern interconnect fabrics.

Physical Characteristics

• Length: 3 meters (fixed-length direct-attach copper).
• Connector Type: QSFP (Quad Small Form-factor Pluggable) compatible ends designed for InfiniBand EDR ports.
• Cable Type: Copper twinaxial assembly with high-quality shielding to minimize crosstalk and EMI.
• Durability: Reinforced strain relief and robust plug housings for repeated insertions and reliable mechanical life.

Electrical & Performance Specs

• Protocol Support: InfiniBand EDR (Enhanced Data Rate), backward compatible with FDR/DDR where supported by host and switch firmware.
• Data Rate: Up to 100 Gbps aggregated bandwidth (EDR-class signaling).
• Latency: Extremely low per-hop latency optimized for RDMA, MPI, and other HPC messaging layers.
• Power Dissipation: Passive operation — minimal additional power draw beyond port signaling.

Performance Tuning and Network Optimization

To extract the best performance from an InfiniBand EDR fabric using HPE 834973-B25 cables, consider both hardware and software-level tuning steps. These optimizations help reduce bottlenecks, maintain high throughput, and improve overall cluster efficiency.

Fabric Topology and Layout

• Design fabrics for minimal hop count in latency-sensitive applications — keep critical nodes as close together physically and logically as possible.
• For multi-rack clusters, use high-speed EDR-capable switches at aggregation points and maintain consistent cable types to prevent mismatched link behavior.

Driver and Firmware Considerations

• Ensure that host channel adapters (HCAs) and switch firmware are updated to versions that support EDR and the specific behavior required by your middleware (MPI, RDMA libraries, storage drivers).
• Validate link speed negotiation — some systems may default to lower speeds if auto-negotiation fails, so check OS and adapter logs for link training messages.

Transport and Middleware Settings

• Tune RDMA and MPI parameters (e.g., eager/rendezvous thresholds, buffer sizes) to match typical message sizes and application patterns for best latency and throughput.
• For NVMe-oF over InfiniBand, align queue depth and IO submission parameters with the NIC/switch capacity to avoid queue stalls.

Comparisons: DAC vs. Optical Transceivers

Choosing between a direct-attach copper cable and an optical transceiver-plus-fiber solution depends on distance, cost, power, and the specific fabric design. Below is a comparison to help guide purchasing decisions.

Advantages of Direct-Attach Copper (DAC)

• Lower upfront cost for short distances (typically under 5–7 meters for DACs).
• No separate transceiver modules — fewer individual components to manage.
• Lower overall power consumption and simplified cabling for dense rack deployments.

Advantages of Optical (Active Optical Cable or SFP/QSFP with Fiber)

• Longer reach over tens to hundreds of meters, suitable for cross-rack and cross-aisle connections.
• Immunity to electrical interference and easier compliance with certain electromagnetic constraints.
• Modular transceivers allow flexible upgrades and replacements independent of cable runs.

Choosing the Right Option

For short-span, high-density rack environments where cost and power are key constraints, the 834973-B25 DAC remains a highly attractive option. For longer spans, or where future-proof flexibility of transceivers is required, fiber-based solutions are preferable.