Ney, no need to call yourself stupid, you are not the only one to get confused with the way mirror works
If you want to mirror the contents of Disk-1 to Disk-0, then you go to the RECEIVING disk setup page (Disk-0 in your case) and set the mirror there (per ex /Disk-1/15 => IP address of the origin (nothing if on the same NASL)/The source to be copied FROM/time of copy in GMT (London time)/)
Be careful for the upper lower case (which are not the same

), do not forget the first "/" and be ware that the last number is the time in GMT when the copy will start.
Last point: if you have files that are on the DESTINATION disk (Disk-0 for you) that are no more on the ORIGIN disk, they will be erased from the destination disk.
To delete the mirror that you set up by error on the wrong disk, just go to the setup page and select the mirror option and validate with nothing on the line.
I hope this helps.