The Red light came on (solid-ish) and the disc unmounted. I did nothing to prompt. ID on device: Chassis SN: DC01603000480 It has 2 drives, 4 TB each. Help? Crisis 
Red light signifies an issue with the RAID in most cases. Open the front cover and see if one of the drives has a red light. If the unit is in RAID0 mode like it was out of the box and a drive fails then the unit will unmount and no longer be usable.
If the device was changed to RAID1 mirror and a drive fails the other working drive takes over and continues to stay mounted so you can access your data.
Thank you. I assume the worst. When I open the front cover, both drives have a red light, as well as the light on the cover.
Interestingly, the fan doesn’t come on either. Is that a classic symptom of this unit?
I guess I should assume it was set up as RAID0. No one seems to know. All super distressing.
Thanks so much for the intel’!
Hi,
I am experiencing a similar issue on my G Speed Shuttle Xl TB3. The chassis has a red light, I open door and all the drives are blinking red. Please advise.
thank you.
Hi biskandrian,
please try resetting the controller settings. In the Restore Factory Default settings screen, check the box beside the controller setting and submit.
If the issue persists:
Shut down the computer. Once powered off, unplug the cable from the XL as well as the power cord so it does a full shutdown. Then switch on the computer again and once the computer is turned on, plug in the power cord to the XL only and wait for it to power on, spin up, beep twice then turn itself back off. Once it has done that then plug the cable back in the computer.
Also check your cables, if you have any other TB devices try them to see if something isn’t happening to the TB on your system. You can also attempt to reset the SMC and NVRAM on your Mac: Resetting the SMC
