FC transceivers & optics

Fibre Channel runs on the same pluggable form factors as Ethernet, but the optics are qualified to FC's own physical-layer standards and labelled with FC's own vocabulary. Picking — or coding — a module for a SAN means speaking that vocabulary.

Wave designations

Reach by generation (multi-mode)

Multi-mode reach shrinks as the rate rises — the reason SAN cabling moved from OM3 to OM4/OM5:

Long-wave optics on single-mode reach 10 km regardless of generation.

Standards behind the optics

The physical layer is defined by the T11 FC-PI series: FC-PI-5 (16GFC), FC-PI-6 (32GFC), FC-PI-7 (64GFC), FC-PI-8 (128GFC). Module identity, rates and DDM follow the same MSA management specs as Ethernet optics — SFF-8472 for SFP+/SFP28 and SFF-8636 for QSFP28 — with FC rates advertised through the rate and application codes.

Module by rate

Vendor lock in SAN switches

FC switch vendors are among the strictest about optics. Platforms commonly validate the module's identity and show a port state such as Mod_Val (validating) or Mod_Inv (invalid) when a non-qualified module is inserted; the port will not come online. Storage arrays and HBAs also ship with qualified-parts lists. The mechanism is the same identity check as on Ethernet switches — see Vendor lock — and the remedy is the same: a module coded with the identity the platform expects.

DDM in a SAN

Because storage traffic is lossless, a marginal optical link shows up as CRC/invalid transmission words and credit stalls long before it shows as a down port. Trend Rx power and Tx bias on ISLs and array ports; a single lane degrading in a 128GFC QSFP28 is the classic silent fault (see Failures).

In CodingBox

CodingBox reads FC optics per SFF-8472/8636, decodes FC rate codes, shows DDM with thresholds, and recodes identity — vendor, part number, rate codes — for the SAN platform you target, with checksums recalculated and a backup in the code database.