D-Link DNS-320L User Manual page 347

Section 4 - Configuration
Go to System Management >> USB Devices. Under USB Storage
Information, you will see detailed information on the device you plugged
into the DNS-320L. You can connect an Android device, but the USB
debugging feature must be enabled.
When the backup is complete, the flashing white LED will become solid
white. Click and hold the USB button at the front for at least 5 seconds to
unmount the USB device for safe removal.
D-Link ShareCenter DNS-320L User Manual 341