I am using an external powered USB-Hub (DUB-H4, DLINK) with two HDDs on my Raspberry Pi. One is a USB 3.0 Western Digital external hardrive and it works fine. The other is a 500GB SATA internal drive connected to an SATA-USB 2.0 Adapter.
When I don't use them, both are spinning down. The problem with the SATA drive is that it seems to disconnect while spinned down and then unmounts itself. The WD drive doesn't show this problem, it simply spins up again when I use it.
Aug 16 16:16:33 raspberrypi kernel: [180527.788276] usb 1-1.3.3: USB disconnect, device number 44
Aug 16 16:16:34 raspberrypi kernel: [180528.249109] usb 1-1.3.3: new high-speed USB device number 45 using dwc_otg
Aug 16 16:16:34 raspberrypi kernel: [180528.350109] usb 1-1.3.3: New USB device found, idVendor=1132, idProduct=4511
Is there a way to fix this, except don't allowing the HDD to spin down?
I think the power supply can't be the problem, because it unmounts itself during standby...