Problem with two external HDD

vinprom

When I add two external USB hard drives (I use the rear USB ports) and I want to back up from NAS to external drive 2 via the Copy/Sync button, the external drive 2 does not appear in the USB volume drop down list, only drive 1 is visible and able to choose.

Initially, the two drives are visible in Storage Manager> External Volumes, but after a while, one disappears ...
I can not fully use 2 external USB hard drives at the same time

#NAS_Jan_2019

Mijzelf

Is it a dual disk problem, or is the 2nd disk the problem. What if you only connect the 2nd disk?

Batou

As far as I heard from, the usb stick with copy, it would only detect the latest one you plug into USB, so may need to plug in again the drive 2.

vinprom

Mijzelf if i connect only one of this hard drives no have a problem...