U.2 and U.3 NVMe Cabling

A U.2 connector does not prove the protocol. That single fact causes more failed enterprise SSD deployments than any other, and it is the reason this page exists.

Are U.2 and U.3 the same thing as NVMe?

NVMe is a storage protocol optimized for solid-state media, commonly riding over PCIe rather than legacy SATA signaling. U.2 and U.3 are enterprise connector and deployment formats — physical and mechanical context, not a protocol guarantee.

A product can match the connector and the drive form factor without providing the protocol support, host support or performance the application needs. That is the whole trap.

What connector do U.2 and U.3 drives use?

U.2 is SFF-8639 — a 68-position connector on the drive or backplane side. SFF-8639 Rev 2.2 states that it supports single-port SATA, dual-port SATA Express, dual-port SAS, MultiLink SAS, or up to four-port PCIe. The specification does not name NVMe at all. NVMe is a protocol that rides the PCIe path; which of those configurations is actually active depends on how the host and backplane are wired, per SFF-TA-1001 — not on the connector.

A U.2 drive needs a separate power lead — always, not usually. SFF-8639 Rev 2.2 defines a dedicated power section (P1–P15), and SFF-9402 Rev 1.1 defines the Root-to-Endpoint POWER pins as "NO WIRE." Power does not travel the data path. It is part of the harness specification, not an afterthought.

Why are the host side and drive side different cables?

A U.2 run goes from a host connector — SlimSAS, MCIO, OCuLink or Mini-SAS HD — to the SFF-8639 drive connector. The connector on each end is different by design, and the cable is built for a direction. A high-lane host port is frequently broken out to two or more U.2 drives as a Y cable.

What should you confirm before specifying a U.2 or U.3 cable?

• Do not assume a physical adapter converts SATA, SAS and NVMe protocols interchangeably. It does not.
• Do not assume U.2 or U.3 physical compatibility means the host platform supports the intended drive behavior.
• Do not assume a product preserves full PCIe generation performance unless generation and lane support are specified.
• Do not assume hot-swap, backplane or enterprise-server compatibility without explicit confirmation.
• Do not assume power is included in the data path. Confirm the drive's power lead.

What U.2 and U.3 assemblies does EPS build to specification?

EPS manufactures U.2 and U.3 harnesses to your specification in Acton, Massachusetts, prototype through production — 10 to 10,000-plus units, QC tested. Length, conductor size and color, stranding, shielding (foil, braid or combination), jacket material (PVC, TPU, FEP, LSZH), temperature and environmental rating, overmolded boots, strain reliefs, latching systems and custom contact configurations are specified by you — as are integrated power leads and multi-drive Y-cable topologies.

Lead time depends on the specification and the volume, and we confirm it with your quote.

Looking for a stocked part rather than a custom build? See available U.2 and U.3 cables at MicroSATACables.

What information does EPS need to quote a U.2 or U.3 cable?

1. What connector is available on the host side?
2. What exact drive type and form factor is being attached?
3. Is the environment a desktop, workstation, server or backplane deployment?
4. What PCIe generation or performance target matters?
5. Is power, hot-swap support or physical mounting part of the requirement?

Frequently asked questions