Because I forget whenever I reload my server.
etc
├── mdadm
│ └── mdadm.conf -- Just need to add the PROGRAM line at the bottom to the system file.
├── mdadm_warning.sh -- Specified by PROGRAM in mdadm.conf. Actually sends the event email using given variables.
├── smartd.conf -- Specify scans for each device in the array. Details within.
└── smartmontools
└── run.d
└── 10mutt -- Sends email when a smart error is detected.