Yes, you can operate two hard drives separately in the GR3660-BA31 by using the JBOD (Just a Bunch Of Disks) mode.

Here are the steps you need to follow:

- Make sure both hard drives (either 2.5" or 3.5" SATA III HDD/SSD) are inserted into the two bays of the enclosure.
- Connect the enclosure to your computer via the USB Type-C or Type-A port.
- Open the RAIDON STATUSGUARD GUI software that is compatible with the device.
- Select JBOD mode in the software interface. In this mode, the two hard drives are recognised as separate, independent drives and can each be used individually.