Class 2 Frame Recovery Timeout Exceeded After Intermittent Port Failure

Expected Recovery Interval

When a Fibre‑Channel link drops briefly, most vendors return the port to full speed after a Class 2 recovery timeout (C2RT) followed by link‑training. In practice:

• 4 Gb/s ports: ~200 ms total (≈120 ms C2RT + 80 ms training)
• 8 Gb/s ports: ~400 ms total (≈250 ms C2RT + 150 ms training)
• Higher‑speed ports scale roughly linearly, but the training phase dominates.

These figures come from vendor firmware logs and controlled pull‑cable tests. The exact value can vary by HBA firmware, switch OS, and whether the device advertises partial link speed during recovery.

Verification Strategy

To avoid skewed throughput metrics, design verification to ignore the first 50–100 ms after a Class 2 recovery completes. A practical approach:

1. Use a port‑monitoring CLI or SDK (e.g., fcspeed, hbaquery, or vendor‑specific SNMP OIDs) to capture timestamps for LINK_DOWN → LINK_UP → FULL_SPEED.
2. Run a throughput test (e.g., fcping or a storage benchmark) that records bytes/s in 10 ms windows.
3. Discard the first n windows after the port reports FULL_SPEED (typically 5–10 windows for a 50–100 ms grace period).
4. Compute the average over the remaining windows to obtain a fair measurement.

If you prefer a continuous measurement, apply a sliding‑window filter that excludes any window where the port reports PARTIAL_SPEED or RECOVERY state.

Vendor‑Specific Parameters to Document

• Class 2 Recovery Timeout (C2RT) – the timer value that triggers retransmission of lost frames.
• Link‑Training Timeout – duration for speed negotiation after C2RT expiry.
• HBA Firmware Version – firmware may expose dynamic C2RT adjustments.
• Switch OS Version – OS may implement early link‑up signaling or enforce stricter training.
• Partial‑Speed Flag – indicates whether the port reports reduced bandwidth during recovery.

Gather these values via the vendor’s diagnostic utilities or SNMP MIBs before performing any throughput validation. Documenting them ensures that any future firmware or OS upgrade can be correlated with observed recovery behaviour.

Next Diagnostic Step

To fine‑tune the grace period or validate the C2RT value, we need the exact HBA firmware and switch OS versions in your environment. Could you provide those details?