u3 · shipping · also SFF-TA-1001, U.3 SSD

U.3

U.3 is the SFF-TA-1001 universal x4 link arrangement for SFF-8639 drive bays that can accommodate PCIe, SAS, or SATA devices with appropriate host support.

Related Observatory article: U.3 on hesela.com

SFF-TA-1001 defines the U.3 link used in tri-mode backplanes. Sharing the SFF-8639 connector does not make U.2 and U.3 equivalent. A bay accepting different protocols does not mean that an individual NVMe SSD also speaks SAS or SATA. [2]

Compatibility is directional. Revision 1.1 requires compliant U.3 PCIe devices to operate in U.2 (Quad PCIe) and U.3 slots, within the available lane width. It does not require a U.3 slot to operate U.2 devices. Verify the particular drive, controller and backplane documentation; systems may implement additional compatibility. [1]

Relations

related

u2, nvme, enterprise-ssd, pcie-lanes

Citations

1. SNIA SFF-TA-1001 Rev 1.1: Universal x4 Link Definition for SFF-8639, section 1 and Table 1-1 (accessed 2026-10-18)
2. KIOXIA: Preparing for Your Storage Future with NVMe SSDs, January 2020 Rev 1.1 (accessed 2026-10-18)

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