Added the 4th disks but it is not RAID1

I fully agree with TeknoJnky. X-Raid2 is the best option you have available. Although there is only one disk devoted to redundancy, in reality, the parity is spread among the four disks, so it will survive the failure of a single drive.

However, I would continue to make a full and complete backup of your data and update it periodically as you never, ever want to trust your data to a single device be it a single drive in a PC or a single raid box. Even if you had two Raid1 volumes, and faithfully copied from one volume to the second, it would not be a reliable backup, for if something happened to the device, you would not only be without your primary, but your "backup".

I would choose x-raid2 myself. Though it is worth noting that two Raid-1 volumes will survive some 2 disk failures and might make it easier to recover from failures with third-party tools. So it does have some advantages (though I would personally rather have the increased capacity of x-raid2).

I agree that you need to back up your data to a separate device. So backing up the first volume to the second volume is not a great idea.

Thank you everybody for your clarifications,

I don't really understand how xraid2 works...

I have 4x3to disks and 8.1tb of space, so 3 disks are used and 1 for redundancy right ?

But what is this redundancy disk ? It has only partial datas in it ? It can't save 8tb on 3tb so what happened if one of the 3 disks died ?

I understand that i need to backup my data on a removable hdd, that's what i planned to do but i choosed raid1 in first instancez because i thought if one disk die i just need to buy another one and replace in the bay.

So why xraid2 is better if i can loose my datas easier ?

Explain me please because i don't have enough disk space to save my datas, and reformat everything in the nas, i need a good reason to stay in this mode.

Also, which disk is the redundant one now in x-raid2 ? which number is the redundant disk ? If i remove it when nas is on, what happened ? Because i want to use it to backup my files before reset factory the nas.

Thanks guys,

There are many resources on the web that explain how RAID works - try Wikipedia as a starting point which I know has good information. Specifically you need to look into RAID-5 as X-RAID2 is an enhanced version of RAID-5 as already mentioned

cyse wrote:
Thank you everybody for your clarifications, I don't really understand how xraid2 works... I have 4x3to disks and 8.1tb of space, so 3 disks are used and 1 for redundancy right ? But what is this redundancy disk ? It has only partial datas in it ? It can't save 8tb on 3tb so what happened if one of the 3 disks died ?

The data is spread amongst the disk. RAID doesn't provide backup, it provides redundancy (except for non-redundant RAID i.e. RAID-0).

Think of X-RAID2 with four equally sized disks like this:
Disks A, B, C and D
A = 1/3 B + 1/3 C + 1/3 D
B = 1/3 A + 1/3 C + 1/3 D
C = 1/3 A + 1/3 B + 1/3 D
D = 1/3 A + 1/3 B + 1/3 C

cyse wrote:
I understand that i need to backup my data on a removable hdd, that's what i planned to do but i choosed raid1 in first instancez because i thought if one disk die i just need to buy another one and replace in the bay. So why xraid2 is better if i can loose my datas easier ?

There is a trade-off more storage space, but any one disk can fail and all data remains intact using X-RAID2 (with 2 or more disks). You have to choose the RAID type that suits you best.

cyse wrote:
Also, which disk is the redundant one now in x-raid2 ? which number is the redundant disk ? If i remove it when nas is on, what happened ? Because i want to use it to backup my files before reset factory the nas.

Parity is spread amongst the disks. Would recommend sticking with X-RAID2. If you remove a disk your array will be non-redundant and an additional disk failure will render your volume dead. To recover data from your volume outside of the NAS you would need X-1 disks (where X is the number of disks in the NAS when the volume is redundant). Also hot-swap is for replacing dead disks or disks you no longer need to use. Anyway a single disk from a 3 or more disk X-RAID2 array is useless by itself for trying to recover data as you need X-1 disks.

Backup to a USB disk or some place else.

Perfect, thanks a lot for your post i understand it better now.

I will go with xraid2 and i will partial save my datas to an external 3tb.

Last question, can i add 2x USB disk on the back of the nas to save the datas ?

Thanks

Yes you can connect multiple USB drives. Best to use ones with their own power supplies or via a usb hub that has its own power supply if the hard drives don't have a power supply.

Thanks,

but the datas are saved incremental or 'full save' each time the task is run for the external drives ?

Okay so if i well understood in two words i can have 1 disk failure and all is ok, i replace it to have redundance again. If i have 2 drives failure at the same time, i lost all my datas on the nas, hopefully i'll have a backup on usb drives? I'm correct ?

Sorry for the mess but i just want to be sure,

That is correct. Never ever trust your critical or important data to a single device, be it a drive in your PC or any Raid device. Something could happen to the device. The Raid is a first line of defense but can never be considered the only line of defense. In addition, even with RAID1 the volumes are formatted in a manner that makes it difficult to read them on a standard PC.

Thank you i understand this.

I thought the format was kind of linux format like ext or something readable quite easily ...

Is this kind of problem with the raid controller happens a lot ? I hope to never encounter this kind of problem...

My important data will be saved externally for sure.