You may check the HDD working modes from the different HDD light statuses on the front of the NVR.

Applies to: All Reolink NVRs

Off HDD light: The NVR hasn't detected the HDD.

Red solid HDD light: The NVR has detected the HDD but has no recordings. 

Red blinking HDD light: The cameras connected to the NVR are recording to the HDD.