I've added another 5 SATA ports, with another JBM585, connected through just 1 PCIe lane.
It works. Performance is just as 'bad' as the motherboard mounted JMB585.
But I now have 11 ports, which means I can switch to the slightly more cost-effective 4Tbyte drives, instead of paying the premium for the 8Tbyte drives (about $50/8tbytes more compared to the 2x4Tbyte drives). It comes at a slight cost in power, but the QVO drives are quite power-efficient. When not in 'use' they hardly use any power.
So now the PCI lanes are _all_ used:
Code:
01:00.0 SATA controller: JMicron Technology Corp. JMB58x AHCI SATA controller
02:00.0 SATA controller: JMicron Technology Corp. JMB58x AHCI SATA controller
03:00.0 Non-Volatile memory controller: Samsung Electronics Co Ltd NVMe SSD Controller SM981/PM981/PM983
04:00.0 Ethernet controller: Intel Corporation Device 125c (rev 04)
05:00.0 Ethernet controller: Intel Corporation Device 125c (rev 04)
06:00.0 Ethernet controller: Intel Corporation Device 125c (rev 04)
07:00.0 Ethernet controller: Intel Corporation Device 125c (rev 04)