When I first set up my Dell PowerEdge T420 to run Unraid, I ran into one of the usual friction points with older Dell servers: the PERC controller defaults to hardware RAID mode.
That’s fine in traditional enterprise environments. But Unraid doesn't like this.
Unraid expects to see disks directly. It wants individual SMART visibility, direct disk access, and full control over how storage is managed. Hardware RAID sits in the middle and abstracts all of that away.
So the PERC had to be converted to IT mode.
This post documents what I did, what I verified before flashing, and what happened afterward.
What's IT Mode?
Most PERC H310 and H710 controllers operate in IR (Integrated RAID) mode, which means the controller presents logical volumes to the operating system rather than raw disks.
For something like Windows Server in a traditional RAID setup, that works perfectly well. For Unraid, it defeats the design philosophy.
Unraid is built around software-managed storage. Each disk needs to appear individually.
Switching the controller to IT mode turns it into a straightforward HBA. No RAID, no virtual disks. It just presents JBOD (Just a Bunch Of Disks)
Just the way Unraid likes it.
Confirm the Controller
Before flashing anything, I confirmed the exact PERC model installed in the server. On my Dell PowerEdge T420, I had the Dell PERC H710 Mini.
The model can be verified through the boot screen, iDRAC inventory, or directly inspecting the controller inside the chassis. It’s worth taking the extra minute to confirm rather than assuming.
Flashing the wrong firmware to the wrong card could spoil your day pretty quickly.
Preparing Before Flashing
Before proceeding, I needed to document the existing firmware version and recorded the controller’s SAS address. Losing the SAS address isn’t catastrophic, but restoring it is cleaner when you already have it written down.
I also made sure the system was on stable power, removed the battery from the RAID controller and, disconnected any unnecessary drives. The goal was to reduce variables and eliminate avoidable risk.
The Flashing Process
Rather than rewriting an already well-documented guide, I followed this process outlined by Fohdeesha. The core steps involve erasing the existing firmware and replacing it with LSI IT firmware, then restoring the SAS address.
Depending on the controller revision, you may need specific versions of sas2flash or additional utilities to wipe existing firmware regions before the flash succeeds.
Verifying IT Mode
After rebooting, I confirmed the controller reported IT firmware rather than IR. The SAS address was restored correctly, and the controller initialized cleanly.
Once Unraid booted, the result was immediate. Each disk appeared individually. There were no virtual RAID volumes. SMART data was visible per drive.
Why Did I Do This?
While the Dell PowerEdge T420 is old and had been discarded from enterprise use, it still has plenty of life left in it.
Flashing the PERC to IT mode removes the layer that conflicts with modern software-defined storage platforms like Unraid. It gives the operating system full visibility into disk health and behavior.
It’s not a beginner task, but it’s a worthwhile one if you’re repurposing enterprise hardware for something more flexible.
For me, this was the step that made the T420 truly compatible with Unraid — and opened the door for whatever its next role might be.