Some guides suggest -d sat+megaraid,N for SATA drives behind a MegaRAID. Try -d megaraid,N first; if that fails, -d sat+megaraid,N may work for some older firmware.
You cannot just guess the number N. You need to know the physical drive ID recognized by the MegaRAID controller.
If your controller presents multiple logical drives (/dev/sda, /dev/sdb, /dev/sdc), then /dev/sda may contain physical disks with IDs 0,1,2 and /dev/sdb may contain physical disks with IDs 3,4,5. The N value is controller-wide, not per logical drive. So you can usually access all physical disks through any logical device, but safest is to use the logical drive that belongs to the same RAID group. When in doubt, try all N on /dev/sda.
Better: use storcli to see which PD belongs to which DG (drive group / logical drive).
Many modern servers use hardware RAID controllers (e.g., Dell PERC / LSI MegaRAID) that present physical drives behind the controller, preventing smartctl from accessing raw device paths like /dev/sda. This feature outlines a robust implementation to detect such controllers, attempt appropriate access methods, and provide actionable fallback steps — including adding support for MegaRAID controllers (e.g., using the megaraid plugin/option) — to surface SMART data where possible.
Once you have identified the drive number (e.g., 0), construct the command using the -d megaraid,N syntax.
Incorrect Command (What caused the error):
smartctl -a /dev/sda
Correct Command:
smartctl -a -d megaraid,0 /dev/sda
(Note: You can usually use /dev/sda or /dev/bus/0 as the device path when using the -d megaraid,N flag, as the flag overrides the path to target the specific disk via the controller.)
To fix this error, you need to tell smartctl to use the megaraid driver and specify which physical disk to query using its N number.
Before using smartctl, you need to map logical drives to physical disk IDs.
If you are writing a script or noting this down for future reference, the clear syntax is:
| Component | Meaning |
| :--- | :--- |
| -d | Device Type Flag |
| megaraid | The driver for Dell PERC / LSI controllers |
| ,N | The physical disk index (0, 1, 2, etc.) |
By ignoring the garbled "39" text and identifying the correct disk index, you will successfully bypass the "Device Open Failed" error and retrieve your SMART data.
Fix: smartctl "Open Device /dev/sda Failed" on Dell MegaRAID Controllers Some guides suggest -d sat+megaraid,N for SATA drives
If you are running smartctl -a /dev/sda on a Dell PowerEdge server and seeing the error "smartctl open device: /dev/sda failed", it is likely because your disks are behind a Dell PERC or MegaRAID hardware controller.
Hardware RAID controllers present a single virtual drive to the operating system, which hides the raw SMART data of the individual physical disks. To bypass this, you must explicitly tell smartctl which physical disk on the controller you want to query using the -d megaraid,N flag. Step 1: Identify the Physical Device IDs
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:
Using smartctl scan: Run sudo smartctl --scan to see if smartmontools can automatically detect the correct mapping.
Using StorCLI: Run sudo storcli /c0 /eall /sall show and look for the DID (Device ID) column.
Using MegaCli: Run sudo megacli -PDList -aALL | grep "Device Id". Step 2: Run the Correct Command
Once you have the Device ID (let's assume it is 0), use the following syntax to pull the SMART report: For SAS/SCSI Drives:sudo smartctl -a -d megaraid,0 /dev/sda For SATA Drives:sudo smartctl -a -d sat+megaraid,0 /dev/sda Many modern servers use hardware RAID controllers (e
Note: Replace 0 with the actual Device ID you found in Step 1. In some configurations, the device node may also be /dev/bus/0 instead of /dev/sda. Why standard commands fail Virtualization: Controllers like the Dell PERC H730 Go to product viewer dialog for this item.
or H755 create a "logical volume." The OS sees the volume, but standard SMART commands cannot reach the physical disks behind the RAID firmware.
Permissive Mode: If the command still fails with minor errors, you can try adding the -T verypermissive flag to ignore mandatory SMART command failures that the controller might be blocking. Troubleshooting Summary
This error occurs because the operating system sees your RAID controller (e.g., a LSI MegaRAID
) as a single logical device, effectively hiding the physical health data of the individual drives behind it
cannot "see through" the controller by default, it fails to open The Fix: Using the -d megaraid,N To access a specific physical drive, you must tell which "slot" or it occupies on the controller. Identify the Device ID ( Use a RAID management tool like
to find the physical drive IDs. For many Dell servers, the first drive is often ID Run the corrected command: with your drive's ID and run the command with sudo smartctl -a -d megaraid,N /dev/sda Use code with caution. Copied to clipboard Example for the first drive: sudo smartctl -a -d megaraid,0 /dev/sda For SATA drives behind the controller: You may need sat+megaraid,N www.couyon.net Why this happens Correct Command: smartctl -a -d megaraid,0 /dev/sda