Rebuilding a RAID Array on a Thecus N4100 Pro

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Back in April I was having a problem with my Thecus N4100 Pro where it was taking a long time to boot up, I’m talking around 8 hours or so. The confusing part was that on the display, it said it was ready, even though it hadn’t moved to displaying status information yet, and when I attempted to login via the web interface it would just hang until it had finished booting up properly.

I could not find anything on the net about it, and I couldn’t get any response from Thecus as to what the cause might be either.

I was doing some research into RAID arrays to try and find out how complicated it would be to move a RAID 5 array to a different RAID controller without rebuilding it when I was reminded that when one disk fails ina RAID 5 array, even though it will continue to function, it will be slower as the data needs to be rebuilt.

This prompted me to have a look at the RAID health through the web interface. It is meant to display on the N4100 Pro LCD if there is a problem with the RAID health however I couldn’t easily see the LCD from where I had it at the time. Unfortunately it was quite slow going accessing the web interface given how slow the NAS was performing in general. When I eventually got it open I discovered that one of the drives had indeed failed.

From what I understood from both the manual and my research online, replacing a drive in the NAS is as simple as pulling out the faulty drive and sliding in a new one. It should then automatically rebuild the data onto the new drive.

This was not the case however. The data simply would not be rebuilt automatically. I read numerous reviews on rebuilding and not one gave any extra steps, they all simply referred to it as simple and painless and only explained having to replace the drive.

The thing that none of them mention though is that after you replace the drive, you MUST set the new drive as a spare before the data will be automatically rebuilt. Once it is set as a spare, it will rebuild the data automatically.

So without further ado, here are some screen shots to help explain:

Raid Configuration Showing New Drive As Spare
Raid Configuration Showing New Drive As Spare

As can be seen in the screen shot above, you need to check the “Spare” check box and then click apply. This tells the NAS that this drive is a spare to be used to rebuild data onto when a drive in the array fails. As a drive has already failed, the NAS will automatically rebuild data onto the drive we have now set as a spare.

Thecus N4100 Pro Rebuilding the RAID
Thecus N4100 Pro Rebuilding the RAID

In the screen shot above you can see the NAS is now rebuilding the data onto the spare drive.

It really is very simple, the problem is both the manual and all of the instructions I could find online simply don’t mention the fact that the drive has to be a spare before the automatic rebuilding will occur.

What gave me the idea to try this was actually a review of one of the higher end Thecus NAS devices that indicated using the spare option to create a 3 disk RAID 5 array with a hot spare so that it would automatically rebuild immediately without needing to replace the drive, thus giving an extra level of redundancy and additional time to replace the dead drive.

Unfortunately I don’t have the address of the review anymore, but that’s it, it really is very simple once you know about the “Spare” check box.

5 thoughts on “Rebuilding a RAID Array on a Thecus N4100 Pro”

  1. Matt,

    Thanks for the instructions on how to do this. You are right in every instruction manual they just say to put the new drive in and let it go. There was no way to tell if the RAID was actually getting rebuilt. I let mine sit for 24 hours thinking that the RAID was getting built but there was no indicator saying it was doing anything. Hopefully this works. Thanks again.

  2. Good luck Matt! I’m glad to hear it helped, I spent days trying to work it out when a drive died, and like you, I tried just putting a new drive in like it said and hoped it was being rebuilt. After a day it didn’t seem to have improved performance wise and there was just nothing to indicate what it was doing.

  3. Thanks for the great article. I was wondering if you turned off your N4100 when performing any of the steps? Or did you swap out the drive with it running?

  4. Wanted to mention that I had to reboot my 4100 pro before it would allow me to mark the new drive that I had swapped out for the failed unit as “spare”. Then it’s just as you stated, Once marked as spare and applied, it began rebuilding. Also a note that my shared files are still available during the rebuild. The only down time I had was during the reboot which took about 90 seconds.

  5. Hey Stu,

    Didn’t see your comments there, sorry about that! I’m glad it helped you out! When I first swapped out the hard drive I turned off the N4100. So when it booted back up, it immediately allowed me to set it as a spare. I have since swapped out another drives without shutting it down and noticed the same thing you mentioned, it had to be rebooted before allowing it to be marked as a spare.

    If you are running a RAID 5 array you should continue to have constant access to everything on the NAS with a single disk failure, it will just be very slow read and write speeds.

    Thanks for the comments and feedback!


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Who Am I?

Matt in Noumea

Matt works sort-of full time running his digital marketing business, TerraMedia. In his spare time though, he loves to travel with his wife, so they usually end up doing a lot of it.
Home is Australia, and while they don’t spend all their time travelling the world, Matt and his wife like to take the time to really explore and get to know a place, even if that means spending a lot longer there than normal tourists might.

You can read more about Matt and his story HERE.

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