Author Topic: Help is needed with TeraStation (Raid + hot spare)  (Read 2701 times)


  • Calf
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  • Posts: 7
Help is needed with TeraStation (Raid + hot spare)
« on: January 05, 2012, 09:36:54 am »



I have a Buffalo TeraStation ES 4TB storage and I've got a couple questions:


I have RAID 5 array on hard drives 1-3 and drive 4 works as a hot spare disk.


1. Does Raid 5 work properly with 3 hard drives overall? In other words, if one of drives 1-3 fails, can the data be recovered by changing the broken hard drive (even if there wasn't the hot spare drive)?

2. Now drive 4 works as a hot spare drive. If let's say drive 1 fails, will TeraStation make a new Raid array from drives 2-4 and leave disk 1 out of it and everything will work seamlessly all the time? When I change drive 1, can I make it a new hot spare disk?


Or am I totally wrong? If I am, please someone tell me how I should do when one of the drives fail (step by step). Cause in that situation I will be in a panic though I have another drive that backups my terastation once a week. It will make me feel comfortable when I know exactly what I have to do in situation when one drive fails. I wanna know how to seamlessly and without losing my data recover the situation that I have raid 5 array with 3 hard drives and one hot spare drive.


Thanks you so much for answering! :)?


  • Calf
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  • Posts: 1
Re: Help is needed with TeraStation (Raid + hot spare)
« Reply #1 on: April 19, 2013, 05:33:19 am »

Hey Aleksiv95,


Some info on RAID5:

In order to build a RIAD5 array, you need at least three (identical) disks. The reason for this is that RAID5 stores your data and so called parity information (error-correction-code) striped among all the disks in your array. This ensures that even if you lose one of your disks, the rest will contain the data stripes (except for one) and the parity information, from which your computer can calculate the missing part of your data. Obviously in case a disk is failed, and the computer has to calculate the missing data, your file access will be slower due to the overhead caused by this calculation. This is the point where the spare disk comes in the picture. It is inteded to replace any disk that fails in your array, restoring full functionality of your array. Thus giving you more time to order and replace the failed disk. This is fully automated, the only thing you have to do is replace the failed disk. After replacing the disk, the original array will be rebuilt, and the hot spare disk that was temporary used for your array will go back to its standby state. This way the RAID5 array with a hot spare ensures continuous access to your files with a short and minimal access speed reduction. This also requires the disks and the controller to be capable of hot-plug.


Now to the TeraStation:

I tested this with my TeraStation, I had configured a RAID5 array with a hot spare disk. Then I removed disk1 from the array to simulate a disk failure. After the spare disk was configured as an active member of the RAID5 array I put back disk1, and performed a rediscovery of the disk. The data on the share was accessible continuously up to this point. Then I formatted Disk1. During a disk operation file sharing is not available, so you will have a downtime when you replace the disk, even if you don't have to reboot your storage (when you have hot-plug disks). I cannot test hot-plug disks, for I have none right now, but I'd be curious to see how that's working.

So my suggestion is to not use hot-spare disk, but use all four disks in a single RAID5, for you have to restart your storage unit anyway. Using a RAID5 consisting of four disk will boost your speed and storage space, while still having the benefits of RAID5 (being able to access data even if one disk is failed).


Further info on RAID 5:

Further info on hot-plug (or hot swapping):


  • Calf
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  • Posts: 5
Re: Help is needed with TeraStation (Raid + hot spare)
« Reply #2 on: March 11, 2019, 08:15:42 pm »
Having a hot spare means that even if you are not present the spare is used so you don't have your data sitting around with no redundancy if you don't notice for a few days because you're on vacation in Patagonia.