Hi Rudy

1- Yes, with all 4 disk plugged in, system does not boot
2- Yes, with the broken disk unplugged, it boots
3 - Yes, raid does not assemble during boot. I assemble manually doing

root@grafico:/home/jose# mdadm --assemble --scan /dev/md0
root@grafico:/home/jose# mdadm --assemble --scan
root@grafico:/home/jose# mdadm --assemble /dev/md0

4 -When I try to mount

   mount /dev/md0 /mnt

mount: wrong file system, bad option, bad superblock in /dev/md0, 
missing codepage or helper program, or other error

     In some cases useful info is found in syslog - try dmesg | tail or 
something like that.

I do dmesg | tail

root@grafico:/mnt# dmesg | tail
[  705.021959] md: pers->run() failed ...
[  849.719439] EXT4-fs (md0): unable to read superblock
[  849.719564] EXT4-fs (md0): unable to read superblock
[  849.719589] EXT4-fs (md0): unable to read superblock
[  849.719616] UDF-fs: error (device md0): udf_read_tagged: read failed, 
block=256, location=256
[  849.719625] UDF-fs: error (device md0): udf_read_tagged: read failed, 
block=512, location=512
[  849.719638] UDF-fs: error (device md0): udf_read_tagged: read failed, 
block=256, location=256
[  849.719642] UDF-fs: error (device md0): udf_read_tagged: read failed, 
block=512, location=512
[  849.719643] UDF-fs: warning (device md0): udf_fill_super: No 
partition found (1)
[  849.719667] isofs_fill_super: bread failed, dev=md0, iso_blknum=16, 
block=32

Thanks a lot for your helping

Rudy Zijlstra <mailto:rudy@grumpydevil.homelinux.org>
11 de octubre de 2017, 12:42
Hi Joseba,



Let me see if i understand you correctly

- with all 4 disks plugged in, your system does not boot
- with the broken disk unplugged, it boots (and from your description 
it is really broken, no DISK recovery possible unless by specialised 
company)
- raid does not get assembled during boot, you do a manual assembly?
     -> please provide the command you are using

from the log above, you should be able to do a mount of /dev/md0 which 
would auto-start the raid.

If that works, the next step would be to check the health of the other 
disks. smartctl would be your friend.
Another useful action would be to copy all important data to a backup 
before you add a new disk to replace the failed disk.

Cheers

Rudy