Designing a Lossless Ethernet Fabric for Storage: What It Takes and Why It Matters

In high-performance environments, the move to Ethernet-based storage isn’t just about raw bandwidth; it’s about predictability, reliability, and control. But Ethernet doesn’t become storage-ready by default. Unlike Fibre Channel, which was purpose-built for lossless transport, Ethernet operates on a best-effort model. That’s fine for email or web traffic, but for storage I/O, even a single dropped packet can introduce delays, retransmissions, or worse: timeouts.

To deliver true lossless behavior over Ethernet, you need more than high-speed switches. It takes intentional architecture, purpose-built protocols, and vendor platforms that simplify the complexity. Arista’s approach to lossless Ethernet fabric design brings all of these together.

Why Standard Ethernet Isn’t Enough

By design, Ethernet prioritizes throughput over reliability. During periods of congestion, switches may drop packets instead of buffering them. For general applications, that’s manageable. But storage workloads (especially block I/O—are not as forgiving). They demand consistent latency and zero loss.

To meet those demands, the industry has developed a suite of enhancements collectively known as Data Center Bridging (DCB). These technologies make Ethernet behave more like Fibre Channel, giving storage traffic the guaranteed delivery it needs.

Key Technologies Behind a Lossless Fabric

Priority Flow Control (PFC – IEEE 802.1Qbb)

PFC allows for per-priority pause control. Instead of pausing all traffic when congestion occurs, PFC targets only the specific class of traffic affected (like your NVMe/RoCEv2 flow) so other services keep moving while critical storage traffic is protected from loss.

Arista Advantage: Full PFC support ensures that sensitive flows get the flow control they need without interrupting the rest of the network.

Enhanced Transmission Selection (ETS – IEEE 802.1Qaz)

ETS assigns guaranteed bandwidth to specific traffic classes. That means your storage traffic won’t have to fight for throughput, even when running alongside video, backups, or general-purpose traffic on the same link.

Arista Advantage: Consistent performance for storage traffic through intelligent bandwidth sharing.

Data Center Bridging Exchange Protocol (DCBx)

DCBx automates the negotiation of DCB settings between switches and NICs, using LLDP to share configuration data. This reduces manual errors, simplifies setup, and ensures all devices are aligned on PFC and ETS priorities.

Arista Advantage: Streamlined, consistent configuration across devices, lowering deployment risk.

Explicit Congestion Notification (ECN)

ECN acts before congestion gets serious. It lets switches warn endpoints about impending congestion, prompting them to reduce transmission rates—avoiding packet drops before they happen. This is especially important in RoCEv2 environments and high-density storage clusters.

Arista Advantage: Integrated ECN support helps maintain flow control without over-relying on pause frames.

Fine-Tuning with QoS and Traffic Handling

Even with DCB in place, QoS configuration matters. You need to identify and mark storage traffic correctly (using CoS or DSCP), assign it to the right queues, and make sure the switching behavior reflects its priority.

In multicast, heavy environments, like distributed storage control planes, ensuring proper multicast handling is also key. Without this, metadata traffic can suffer, even if the primary data flows are optimized.

Storage Workloads Are Not Like Compute Workloads

It’s important to understand that storage and compute traffic behave differently—and have very different tolerance levels.

• Compute traffic (e.g., app services, web queries) can handle some jitter or packet loss and is often bursty.
  
  
• Storage traffic, especially block-level traffic from VMs or databases, is sensitive to microbursts, intolerant of jitter, and highly susceptible to incast congestion, where many storage nodes respond simultaneously to a single request.
  
  

This difference places unique demands on the network:

• Deep Buffers: Required to absorb microbursts and protect against incast collapse.
  
  
• Granular Flow Control: PFC and ECN are more than nice-to-haves;  they’re required.
  
  
• Consistent Low Latency: Storage traffic can’t afford the variability that general-purpose fabrics might allow.
  
  

Arista’s R-series switches are purpose-built for this level of performance. With ultra-deep buffers and full support for DCB and congestion controls, they’re an ideal match for storage-heavy environments.

Simplifying It All with Arista EOS and CloudVision

Even the best-engineered hardware needs to be usable. That’s where Arista EOS and CloudVision shine.

• EOS simplifies complex configurations with intuitive commands and programmatic interfaces.
• CloudVision gives you real-time insight into congestion points, queue depths, and buffer utilization -  data that’s critical for tuning and troubleshooting.

Together, these platforms transform a technically demanding fabric into one that’s manageable, observable, and operationally stable.

The Added Benefit of Cut-Through Switching

Many Arista switches also use cut-through architectures, forwarding packets before they are fully received. This dramatically reduces latency. It's a big win for performance-sensitive storage traffic.

In Summary: Building a Storage-Ready Ethernet Fabric

Designing a lossless Ethernet fabric is about more than plugging in fast switches. It’s about understanding what storage traffic needs, implementing the right protocols, and tuning the environment for predictability and performance.

Arista provides more than just hardware. It delivers a complete framework (including deep buffers, congestion-aware switching, automation, and visibility), so your Ethernet fabric works as reliably for storage as Fibre Channel ever did...only now it’s faster, simpler, and more scalable.

If you’re looking to unify your storage and data networks without sacrificing performance, Arista offers the tools to make that transition seamless and safe.

Table 2: Lossless Ethernet Design Checklist