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.
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!
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.
DELL-Charles R
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4.7K Posts
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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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2 Posts
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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)