Okay with some troubles, I managed to understand something.
What I did after installing mbadm is using the command sudo fdisk -l
After that i got a bunch of data, but I guess this is what I needed to know.

Disk /dev/sdc: 3.7 TiB, 4000787030016 bytes, 7814037168 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 33553920 bytes
Disklabel type: gpt
Disk identifier: 560070A2-CB61-4416-BC11-E4F7C2E28388

Device          Start        End    Sectors  Size Type
/dev/sdc1        2048    4196351    4194304    2G Linux swap
/dev/sdc2     6293504 7811938303 7805644800  3.7T Microsoft basic data
/dev/sdc3  7811938304 7814037134    2098831    1G Microsoft basic data
/dev/sdc4     4196352    6293503    2097152    1G Microsoft basic data


After this I tried to run --examine:

ubuntu@ubuntu:~$ sudo mdadm --examine /dev/sdc
/dev/sdc:
   MBR Magic : aa55
Partition[0] :   4294967295 sectors at            1 (type ee)


ubuntu@ubuntu:~$ sudo mdadm --examine /dev/sdc1
/dev/sdc1:
          Magic : a92b4efc
        Version : 0.90.00
           UUID : 2da381ee:0105a2ee:40130e04:e0c90235
  Creation Time : Fri Oct 20 16:57:14 2017
     Raid Level : raid1
  Used Dev Size : 2097088 (2048.28 MiB 2147.42 MB)
     Array Size : 2097088 (2048.28 MiB 2147.42 MB)
   Raid Devices : 4
  Total Devices : 3
Preferred Minor : 0

    Update Time : Fri Oct 20 16:57:32 2017
          State : clean
Internal Bitmap : present
 Active Devices : 3
Working Devices : 3
 Failed Devices : 1
  Spare Devices : 0
       Checksum : aca4dbd2 - correct
         Events : 6


      Number   Major   Minor   RaidDevice State
this     1       8       33        1      active sync   /dev/sdc1

   0     0       8       17        0      active sync
   1     1       8       33        1      active sync   /dev/sdc1
   2     2       8        1        2      active sync   /dev/sda1
   3     3       0        0        3      faulty removed


ubuntu@ubuntu:~$ sudo mdadm --examine /dev/sdc2
/dev/sdc2:
          Magic : a92b4efc
        Version : 1.0
    Feature Map : 0x1
     Array UUID : 4bc3cfef:db0ae9ef:2bceeae9:ac2bbee2
           Name : 1
  Creation Time : Mon Nov  7 13:04:44 2016
     Raid Level : raid1
   Raid Devices : 2

 Avail Dev Size : 7805644528 (3722.02 GiB 3996.49 GB)
     Array Size : 3902822264 (3722.02 GiB 3996.49 GB)
   Super Offset : 7805644784 sectors
   Unused Space : before=0 sectors, after=256 sectors
          State : clean
    Device UUID : d23ca413:64d7dec5:d938d9d6:b11d2d26

Internal Bitmap : 2 sectors from superblock
    Update Time : Fri Oct 20 08:43:02 2017
       Checksum : 5124c394 - correct
         Events : 3


   Device Role : Active device 1
   Array State : AA ('A' == active, '.' == missing, 'R' == replacing)

ubuntu@ubuntu:~$ sudo mdadm --examine /dev/sdc3
mdadm: No md superblock detected on /dev/sdc3.
ubuntu@ubuntu:~$ sudo mdadm --examine /dev/sdc4
mdadm: No md superblock detected on /dev/sdc4.
ubuntu@ubuntu:~$

2017-10-21 12:22 GMT+00:00 Francesco Tomadin [off-list ref]:

Thanks for the reply!
First of all, I'll try to express myself in the best way I can :) (I'm
actually impressed that you realized my main language)

As you said, the nas won't boot up, it's stuck from yesterday. I'll
probably have to plug out the electricity since it doesn't work at
all. At the moment when I try to log in in the control panel it says
is performing file system consistency check. I'm not even sure if
unplugging right now will make the things even worse.

When you ask me to run those commands, to be honest I wouldn't even
know where to start, from what I tried to do in the last 2 days, I was
only able to see the disk partitions, and nothing more.


2017-10-21 13:25 GMT+02:00 Anthony Youngman [off-list ref]:

quoted

On 21/10/17 11:46, Francesco Tomadin wrote:

quoted

As title says, due to a bug in the WD nas, it started creating
infinite shares folder.
At the moment I can't access my NAS anymore, so I decided to try
ubuntu to recover my data.
I tried to follow some guides and to check stuff but seems like
(especially for my NAS) stuff like this doesn't exist.
I don't even wanna try to do stuff on my own since as you can clearly
see I'm not a linux user I don't even understand what's going on.

PS: My nas had 4 slot, one of them was in JBOD format, and with ubuntu
I could easily access the data without problem.

Tried to use some mdadm command but It gave me some "strange" errors
which I would ever try to "fix" on my own.
Tried to give a last chance to my nas yesterday but it's stuck at boot.
Please if someone could really help me task to task because I really
really don't know what to do anymore.

Have you read the raid wiki? Is there any chance you could run the --detail
and --examine commands? (Yes I get you may have problem finding the disks to
be able to run the commands on them! :-)

https://raid.wiki.kernel.org/index.php/Linux_Raid

You might have to take the disks out of the NAS, or force the whole thing
into JBOD mode, but again if it won't boot, that might not be possible ...

quoted

Sorry for my poor english It's not my first language.

Better than my foreign languages! If you can't express yourself clearly in
English, then post bi-lingual. I'm guessing your first language is Spanish
or Italian, which I don't understand, but there are probably people who do.
But you need to use as much English as possible to get the best help.

Cheers,
Wol