drives not visible on SCU ports - Supermicro X9SRA

[ljwobker]

I'm stumped here - I've got a supermicro X9SRA motherboard (2x 6gbps SATA + 4x 3gbps SATA on native board, then 4x 3gbps on the SCU) but for some reason I can't seem to reliably get drives to appear either in BIOS or in the OS (Ubuntu 16.04) when they're attached to the SCU. The drives are good, the cables are good, and with different drive combinations I've been able to get things to work reliably on the SCU ports. At this point I'm really looking for help troubleshooting or what to look for... my plan is to end up with two SSDs on the "Fast" ports for the OS, then six 2TB spinners for bulk storage and an optical DVD drive as some of my windows VMs still need optical access. I can't seem to figure out what the secret knock is to get all these spinning drives to be recognized. Is there some limitation (number of drives, type of drives, etc.) with the board/SCU/BIOS that I'm totally unaware of?