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November 26th, 2025 13:50
Dell MD3420 - RAID controller module replacement
Hello everyone.
Has anyone had any experience replacing the RAID controller module on a Dell MD3420? Or a similar storage system?
Let me explain the problem. I have a Dell PowerVault MD3420 with 24 drives containing data.It has two 12G-SAS-4 controller modules (E02M005). One of these modules started to fail a system error: when powered on, the module goes through a check, reaches the Cache Backup Device, receives the UNKNOWN status, and then goes offline. Switching it online repeats this process.
Currently, the storage system is running on one controller. Fearing that the tests might affect the working controller, I decided to replace the faulty one.
They no longer produce or sell new modules, so I bought a used storage system with two modules instead. Unfortunately, one module is faulty, but the other is perfectly functional, passes all internal tests, and I updated its firmware. Now it's completely identical to the one installed on the working storage system. I couldn't find any RAID settings on it.
Therefore, the question is:
1. After speaking with one of the server hardware suppliers, I was assured that replacing these modules was "as easy as pie." I turned them off, removed them, inserted them, turned them on, and everything worked automatically. Since I've never encountered this before, I'm concerned about the safety of the RAID settings, and indeed the data itself, on the working module of the storage system I'm using. Is it really that simple?
2. Another supplier explained the module replacement by saying that after installing a new module in the working storage system, automatic synchronization must be performed. I didn't find any menus or options related to "automatic synchronization" in the DELL Modular Disk Storage Manager program, only time synchronization. In other words, Not only did I insert it, but I also need to run some kind of synchronization?
If anyone has had this experience, please share it!
Thank you!
DELL-Charles R
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November 26th, 2025 21:43
The MD3420 controllers are hot-swappable, and Dell supports replacing a failed controller while the array is powered on as long as the other controller is healthy and the system is not in a critical state.
Verify the Good Controller is Optimal
In Modular Disk Storage Manager (MDSM), check:
Controller status = Optimal
No active Recovery Guru alerts (except the failed controller).
Insert the Replacement Controller
Hot-plug the new controller into the empty slot.
Ensure it is the same model (E02M005) and firmware matches the existing controller.
Automatic Synchronization
The new controller will pull the configuration from the disks and the active controller automatically.
There is no manual RAID sync option—the process is handled internally.
Monitor in MDSM
Watch for “Configuration Mismatch” alerts.
Do NOT initialize disks.
miniAstartes
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November 29th, 2025 14:32
So, today I replaced the controller module.
Just in case, I turned off both the MD3420 and the MD1220 expansion shelf (sorry, I didn't mention that I also have an MD1220 connected to the MD3420).
However, after installing the new module to replace the faulty one, it refused to work and switched to offline mode without any system errors. The module's information said "Unable to retrieve latest data; using known state." I tried turning it on (online mode), and it immediately switched to offline. Also, in the Battery Packs information, the status was "Learning" for both modules. While I was searching for information about this and wondering what to do next, the Battery Packs switched to Optimal mode. I manually switched the module (online) again, and the controller started working. All errors in the storage system disappeared (there were errors with NTP and network settings on the "new" module), and I saw that one of the RAID arrays was now running on the "new" module.
What a great experience!
@DELL-Charles R - Thank you very much!
P.S. I replaced the battery (CR2032) on the "new" module, which stopped it from booting in standard mode. To boot it, connect it to your computer using a mini USB cable (the port is on the back of the module) and an RS232 adapter. Launch PuTTY, connect to the COM port, press space, and type C (there will be an option and C for continue). After that, the module will boot. I've included this information just in case anyone doesn't know.
(edited)