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I notice a lot of U.2 adapters on sale, seem to show what looks like a U.2 to SFF-8643 cable, or SFF-8643 PCIe connector/adapter, instead of the expected U.2 to SFF-8639 cable or SFF-8639 PCIe connector/adapter. (Example 1 ; Example 2)

  1. Are SFF-8643 and SAFF-8639 cables, connectors and adapters electrically compatible? Or are SFF-8643 deployed as 2 incompatible variants ( for use with SAS and U.2) that have the same physical form factor but are electrically incompatible?
  2. If compatible, does this mean I can plug any U.2 2.5" SSD into any SFF-8643 baseboard/PCIe adapter (not just into SFF-8639 connectors/adapters), provided the cable/adapter has physically compatible terminations at both ends? Would HBAs such as LSI-93xx with SFF-8643 connectors be compatible? Alternatively, what criteria apply for compatibility, how to check?
  3. SFF-8643 with SAS is typically used with (eg) 4 way fanout cables. What are the implications for SFF-8643 fanout if used with U.2 drives? Is fanout possible with U.2 drives (albeit at reduced individual bandwidth)? Or are fanout cables only made for SFF-8643 to SAS/SATA, not SFF-8643 to U.2?

I've looked but can't find a definitive answer, either on Google, or on this site, or on superuser.com. There are similar questions but none specifically clarify these points

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