I have OMV5 installed on my Raspberry Pi 4 with two USB drives connected to both USB3.0 ports. It boots up fine but after a few hours, one of the drive no longer responds. When I run sudo lsblk, I no longer see sda anymore until I reboot. Any ideas?
I'd put both of them on the powered hub just to free up power for other things you might want to plug in, there's a hard limit of 1.2A combined total to all the USB ports on the Pi. But just putting the drive that keeps shutting off on there would be a good first troubleshooting step.
The 2 ports (all 4 of them actually) share a single PCIe lane to the processor, so theoretically a single USB3 connection can make full use of the available bandwidth.