AOC vs DAC for InfiniBand HDR 200G: Which Cable Should You Buy in 2026?
Every 200Gb/s InfiniBand HDR fabric comes down to one recurring purchasing decision: connect each port with a Direct Attach Copper cable (DAC) or an Active Optical Cable (AOC). Both terminate in the same QSFP56 form factor and both negotiate the same HDR link, but they behave very differently in reach, power draw, airflow, and total deployment cost. This guide summarizes how experienced cluster builders make the call, and where surplus genuine OEM stock changes the economics entirely.
The Short Answer
Use DAC inside the rack, AOC everywhere else. Passive copper is cheaper and draws essentially zero power, but at 200G PAM4 signaling it runs out of headroom around 2 meters (3m with heavier gauge at reduced margin). Any spine-to-leaf run, row crossing, or overhead tray route belongs to optics. That is why the 35m to 100m MFS1S00-V series AOCs are the workhorse interconnect of AI training clusters and HPC supercomputers.
Side-by-Side Comparison
| Factor | DAC (Passive Copper) | AOC (Active Optical) |
|---|---|---|
| Maximum reach at HDR 200G | ~2m reliable (3m marginal) | Up to 100m (OM3 MMF) |
| Power per end | ~0W (passive) | ~4.35W with retiming |
| Cable diameter / bend | Thick, stiff, heavy | ~3mm, light, flexible |
| Airflow impact | Significant in dense bundles | Minimal — better rack cooling |
| Bit error rate margin | Tight at HDR speeds | Strong, retimed at both ends |
| Typical use | Server-to-leaf in same rack | Leaf-to-spine, row-to-row, tray runs |
| Genuine OEM price (typical distributor) | $150–$400 | $1,400–$2,800 retail |
Why Reach Dominates the Decision
In a fat-tree topology, spine-to-leaf connections routinely span 40 to 60 meters once cables are routed through raised floors and overhead trays rather than straight-line distance. A 50m AOC such as the MFS1S00-H050V covers a full data center row; the 80m, 90m and 100m variants handle inter-row and inter-cage links. Copper simply cannot participate in these paths at 200G, so the real question is never "AOC or DAC" for the fabric as a whole — it is how many of each the topology requires. Most HDR clusters end up roughly 30% DAC (in-rack) and 70% AOC (everything else).
Power and Cooling Math
An AOC draws about 4.35W per end with retiming. Across a 1,600-cable fabric that is roughly 14kW of interconnect power — not trivial, but the thin 3mm optical jacket dramatically improves rack airflow versus bundles of thick copper, which recovers much of that energy in reduced cooling load. Dense HDR bundles of DAC can block enough rear-door airflow to raise switch inlet temperatures several degrees; optics avoid that penalty entirely.
Genuine OEM vs Compatible: The Hidden Failure Mode
NVIDIA Quantum switches and ConnectX-6/7 adapters perform firmware-level cable authentication at link initialization. Third-party "compatible" AOCs often pass a basic link-up test, then produce firmware warnings, failed BER certification, or intermittent link flaps under sustained 200G load — the kind of fault that surfaces halfway through a multi-day training run. Genuine MFS1S00 cables pass every firmware check without workarounds, which is why hyperscalers specify OEM optics even at 3-4x the compatible price.
Where Surplus Changes the Economics
The usual objection to genuine OEM optics is price: $1,400 to $2,800 per cable at distributor retail, with 8–14 week lead times since the MFS1S00-V series entered its end-of-life cycle. Project-liquidation surplus removes both problems at once. Our current inventory — 12,000+ factory-sealed, never-installed MFS1S00-V cables from a cancelled enterprise deployment — sells for $140 to $280 per unit, below what most compatible clones cost, and ships same day from US stock with free ground shipping.
| Length | Part Number | Our Price | Typical Retail |
|---|---|---|---|
| 35m | MFS1S00-H035V | $140 | $1,400 |
| 50m | MFS1S00-H050V | $205.20 | $2,052 |
| 60m | MFS1S00-H060V | $230 | $2,300 |
| 80m | MFS1S00-H080V | $240 | $2,400 |
| 90m | MFS1S00-H090V | $260 | $2,600 |
| 100m | MFS1S00-H100V | $280 | $2,800 |
Building or expanding an HDR fabric?
All six lengths are in stock, factory sealed, genuine NVIDIA Mellanox. Free US ground shipping, same-day dispatch before 2 PM CST, volume discounts from 10 units. Call Sean at 567-485-8018 or request a quote online.
Get Bulk Pricing →Frequently Asked Questions
Can I mix AOC and DAC in the same HDR fabric?
Yes. The switch negotiates each link independently. Standard practice is DAC for in-rack server-to-leaf connections and AOC for all longer runs.
Do MFS1S00-V cables work for 200GbE as well as InfiniBand?
Yes. The V suffix indicates VPI support: the cable carries InfiniBand HDR 200G and 200G Ethernet, making it usable in both fabrics.
Is OM3 multimode fiber enough for 100m at 200G?
For AOCs the fiber is factory-terminated inside the assembly and rated end-to-end by NVIDIA — the 100m H100V is fully specified at 200Gb/s over its integrated OM3 MMF.