Difference between SAS multilane, direct-attached HDD and expander backplane?

Solution 1:

Yes, that's all correct. I suppose it's not clear from the Supermicro product pages.

SAS SFF-8087 is a 4-lane multi-connection transport. It's typically used by RAID controllers and disk backplanes. You probably want to avoid anything that requires fanout cables. Expander backplanes can have some problems, depending on what types of disks and controllers will be in use.

Also this: How exactly does a SAS SFF-8087 breakout cable work? + RAID/connection questions

Solution 2:

The cable you'll use is dependent on the drive backplane and the disk controller you use. If both of them are SFF-8087, you can get an SFF-8087 straight cable, otherwise you might have to use a fan-out cable.