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Thecus N5550 with 6th drive mod

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Hello unRAID community,


This isn't a conventional build but rather re-using hardware and re-purposing it for use with unRAID.


We also modify the N5550 chassis to be able to run a 6th drive in what should only be a 5-bay NAS. 


I am sure there are many N5550 owners out there that may find this useful.

You can also check out the full blog post here: https://www.vskilled.com/2019/07/unraid-on-thecus-n5550-with-6-drives/


------------- Background -------------

Anyone with Thecus NAS devices knows that the operating system “ThecusOS” has been practically abandoned. The vendor came out with “OS7” but it never fully finished and development died somewhere along the way. It also did not fully support the N5550 and many other models. Owners were left with unsupported devices. This was fine with me for a while since I never really used the management interface except when configuring or troubleshooting issues. However after a couple years now the interface is very outdated and I was looking for something more modern.

I did upgrade one of my N5550’s to “ThecusOS7”, a beta version. It was able to install and it appeared to be functional however I was unable to create a RAID volume. Which means I could not use it for much of anything. Not to mention it was clunky and the older UI actually seemed to be more functional. It was clear that OS7 was just trying to mimic Synology’s DSM, but lacked all the polish. My attempts to downgrade were unsuccessful and I had pretty much bricked the NAS.


------------- unRAID on N5550 -------------


  • unRAID operating system on a Thecus N5550
  • Stable
  • Easy to install, maintain, and update
  • Link bonding and LACP is working
  • No issues with detecting the IO or network drivers


  • Unsupported configuration – technical expertise highly recommended
  • HDD activity lights do NOT work (blue “on” light, but no flashing of activity, or red error lights)
  • LCD screen does NOT work (stays stuck on “Starting health checks”)
  • Slower write speeds due to how unRAID works



------------- 6th Drive Mod for N5550 -------------

This mod will allow you to add a 6th drive to your 5-bay N5550 NAS using the SATA and 4-pin power slot after removing the 1GB DOM module.


Before we begin…

  • AT YOUR OWN RISK! Unsupported and may void your warranty.
  • Backup and migrate your data. ALL DATA WILL BE DESTROYED!
  • Remove the 1GB SATA DOM module
  • Bootable USB (32GB recommended) to be used for the unRAID OS
  • Change the boot order (Press F2 during POST)
  • Install a 6th drive




Inside the chassis of a Thecus N5550:


When you open the case of your N5550 you will see the above. We can see a internal SATA port and 4-pin power slot. 


1 - Removing the SATA DOM module: The ThecusOS is saved to the 1GB DOM module so if you need to restore then you can simply re-install the DOM, switch your boot order back, and be back to original state. Carefully remove the DOM and set it aside.


2-  Options are now available: After removing the DOM module this free’s up a SATA and 4-pin floppy power port on the motherboard. This can be used for a SSD or HDD to boot an OS or increase your drive pool to 6 drives. Either is a good option. The choice is yours.


3 - Chassis modification: The trouble with the 6th drive mod is that there is almost no room inside the case. You might be able to squeeze a 2.5″ drive in there but certainly not a 3.5″ drive. My solution was to cut the case and simply have the extra drive outside the case. It’s not pretty but it works. If you’re considering this change for your N5550 then I am sure that you’re on the same page.




Removed DOM and install the new cables. CAREFULLY cut the venting of the top-right of the case just enough to feed the cables through.


The finished modification install. I also zap-strapped the cables to prevent them tugging at the socket and possibly causing damage or coming loose. 



Again, it's not pretty... but it works. 6-bay N5550!


Hopefully this helped for owners of Thecus products. The hardware is still usable. Just rip out that DOM module and install whatever you want.

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