To drop a device you want to:
- remove all databases from device
- drop the device from the dataserver (via sp_dropdevice)
- if the device is a file out in the OS then remove said file
If your disk init is failing with a message about a device already existing then it's usually a) the device already exists (sp_helpdevice NRD_DATA_001) and you need to first sp_dropdevice NRD_DATA_001 or b) the OS file exists and you need to rm it. At this point it's hard to tell which is the case because we haven't been given the actual error message.
For future reference, please post the entire output/error message as there are usually some key details in said message.