I was recently reviewing some backplanes and I found that some backplanes supports SAS/SATA and NVMe altogether. I saw several combinations. One backplane I saw supported few ports dedicated to SAS and few for NVMe. The other I saw that supported SAS/SATA+NVMe.
I do understand that you can use SAS and SATA drives in SAS ports. However, how is it possible that SAS and U.2 ports are same on the backplanes? But maybe different pinouts probably.
Or like how SATA drives are compatible with SAS ports, is it the same thing for U.2 port? I mean can a U.2 port accept U.2 drives/SAS/SATA drives as well? Just signaling is different for U.2 (PCIe) and SAS for the SAS/SATA.
Next to this, I saw that few backplane uses 2x molex connectors for powering up 2/4/6 and even 8 drives. My question is are 2x molex connectors sufficient enough to power like 8xSAS/SATA or U.2 drives (2.5 inch)?
Normally you’d see dedicated SAS/SATA ports/connectors and dedicated U.2/U.3 ports/connectors. I know of backplanes that only have cable connectors and you choose the cable according to the connector standard you want to use. I am unsure how the standards are defined exactly though. Can you provide a name or link to the backplane you mentioned?
Molex is rated for 12V with 11A per pin, meaning at least 132 W. Divide that with what common drives consume and you see that this should be enough to power them. 8 are fine, 10 should be.
Same SFF-8639 connector on the drive side for SAS, U.2 and U.3, but using different sets of pins.
The key point is what the backplane takes from the motherboard side:
If it has separate cables for SAS and NVMe, then it is a U.2 backplane. You plug the SAS/SATA ports into a SAS HBA and the NVMe ports into PCIe lanes, cabled from whatever the motherboard provides, or a PCIe switch. Any drive goes, SAS/SATA, U.2 or U.3.
If SAS and NVMe go through the same cables, then it is a U.3 backplane, and you use it with a Tri-Mode HBA. On the drive side you can use SAS/SATA or U.3 drives, but not U.2.
