If you encounter the error Smartctl open device: /dev/sda failed: DELL or MegaRaid controller, please try adding '-d megaraid,N' , it means smartctl cannot directly talk to your hard drives because they are hidden behind a (like a Dell PERC). To fix this, you must tell smartctl exactly which physical drive to look at using the -d megaraid,N flag. Why This Error Occurs
sudo apt install smartmontools
To resolve this issue, you need to inform smartctl about the presence of the MegaRAID controller and the logical drive number (N) associated with the disk drive you want to monitor. You can do this by adding the -d megaraid,N option to the smartctl command. If you encounter the error Smartctl open device: