SAS disks vs. SATA connectors. How does it work?

[DaveLTX]

one thing im curious on is the sas ssd's that also have the u.2 connector, but dont require a u.2 connection to work.

Like the "SDLL1MLR-038T-CDA1"

U.2 specifies using SFF 8639 for PCIe NVMe SSDs, but its the same exact as SFF-8680... which is basically just 8639 used for SAS

Those SAS SSDs fit in both 8639 and 8680 but absolutely won't work on cables meant for PCIe. PCIe uses all four lanes of the 8639 plug while SAS is usually seen with only 1 lane. That's why you see both 8643 to U.2 cables that is only one ended on the U.2 side while 8643 sas cables split one four lane 8643 (also known as mini sas?) into 4x single lane "8639" (Note : Seems like 8639 is TWO SAS/SATA lanes or also known as dual ported but of course sata doesn't have allow that and dual porting is usually used for redundancy reasons)

NOTE : U.2 is dual protocol but the backplane or cable must be specifically wired for U.2 or SAS. U.3 fixes that but in the grand scheme of things, U.3 is not gaining traction so I more or less ignore it
ALSO NOTE : U.3 drives work in U.2 hosts but not the other way round. Not that it matters anyway, U.3 was mostly made to help broadcom push those stupid expensive tri mode HBAs

 

[kryten]

i had 70 to unlock, its just when it came to testing them 8 at a time some dropped off, thought it may have been the top layer of pins causing an issue. but i think some are just faulty.

 

[DaveLTX]

i had 70 to unlock, its just when it came to testing them 8 at a time some dropped off, thought it may have been the top layer of pins causing an issue. but i think some are just faulty.

SAS?

 

[kryten]

Yes