Well, it turns out I should not have bothered to solder the other two SAS headers. It seems only the first SAS header works.
This probably would have been obvious had I engaged my brain and looked at BIOS/lspci earlier:
So the chipset only offers 6 SATA ports: 2 already on the motherboard + additional 4 via the first SAS header.
There is nothing in BIOS about the second SAS header ("HDD 4-7") and plugging drives into the SAS port does nothing. Drives aren't detected in BIOS or in the OS. Same with the third SAS header ("HDD 8-12").
There was something in the chipset datasheet about an external option ROM required for the SAS controller. It seems this is missing. So the most benefit you can get is 4 additional SATA 2 (3Gbps) drives from the chipset. If you're full on the PCIe slots and you desperately want to add more drives, it might be worth the effort, but overall I'd say: "nah"
This probably would have been obvious had I engaged my brain and looked at BIOS/lspci earlier:
Code:
00:1f.2 SATA controller: Intel Corporation C600/X79 series chipset 6-Port SATA AHCI Controller (rev 05)
09:00.0 Serial Attached SCSI controller: Intel Corporation C604/X79 series chipset 4-Port SATA/SAS Storage Control Unit (rev 05)
There is nothing in BIOS about the second SAS header ("HDD 4-7") and plugging drives into the SAS port does nothing. Drives aren't detected in BIOS or in the OS. Same with the third SAS header ("HDD 8-12").
There was something in the chipset datasheet about an external option ROM required for the SAS controller. It seems this is missing. So the most benefit you can get is 4 additional SATA 2 (3Gbps) drives from the chipset. If you're full on the PCIe slots and you desperately want to add more drives, it might be worth the effort, but overall I'd say: "nah"