To use the "-d megaraid,N" option, you'll need to determine the logical drive number or physical drive number on the MegaRAID controller. You can do this by:

Before you can run the command, you need the "Device ID" or "Physical Disk Number" for each drive. You can find this using the following tools:

After initiating a test, monitor its progress with:

# List physical drives and their IDs storcli /c0 /eall /sall show Use code with caution.

For MegaRAID/Dell PERC, the most reliable tool is storcli (successor to megacli ):

The error message often hints at the problem:

To access the S.M.A.R.T. (Self-Monitoring, Analysis, and Reporting Technology) data of your disks, you must tell smartctl how to communicate through the RAID controller. The Solution: Using -d megaraid,N

Here's an example:

Troubleshooting "smartctl open device dev sda failed" on Dell/MegaRAID Controllers

Here are some examples of using smartctl with the "-d megaraid,N" option:

The error smartctl open device: /dev/sda failed: DELL or MegaRAID controller, please try adding -d megaraid,N is not a bug—it is a sign that you need to tell smartctl which physical drive behind the RAID controller to query.