Hi Adam

root@grafico:/mnt# cat /proc/mdstat
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] 
[raid4] [raid10]
md0 : inactive sdd1[3] sdb1[1] sdc1[2]
       2929889280 blocks super 1.2

unused devices: <none>


root@grafico:/mnt# mdadm --manage /dev/md0 --stop
mdadm: stopped /dev/md0


root@grafico:/mnt# mdadm --assemble /dev/md0 /dev/sd[bcd]1
mdadm: /dev/md0 assembled from 3 drives - not enough to start the array 
while not clean - consider --force.



root@grafico:/mnt# cat /proc/mdstat
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] 
[raid4] [raid10]
unused devices: <none>

At this point I´ve followed the advise using --force

root@grafico:/mnt# mdadm --assemble --force /dev/md0 /dev/sd[bcd]1
mdadm: Marking array /dev/md0 as 'clean'
mdadm: /dev/md0 has been started with 3 drives (out of 4).


root@grafico:/mnt# cat /proc/mdstat
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] 
[raid4] [raid10]
md0 : active (auto-read-only) raid5 sdb1[1] sdd1[3] sdc1[2]
       2929889280 blocks super 1.2 level 5, 512k chunk, algorithm 2 
[4/3] [_UUU]
       bitmap: 0/8 pages [0KB], 65536KB chunk

unused devices: <none>


Now I see the RAID, however can't be mounted. So, I'm not sure how to 
backup the data. Gparted shows the partition /dev/md0p1 with the used 
and free space.


If I try

mount /dev/md0 /mnt

again the output is

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

If I try root@grafico:/mnt# mount /dev/md0p1 /mnt
mount: /dev/md0p1: can't read superblock

And


root@grafico:/mnt# dmesg | tail
[ 3263.411724] VFS: Dirty inode writeback failed for block device md0p1 
(err=-5).
[ 3280.486813]  md0: p1
[ 3280.514024]  md0: p1
[ 3452.496811] UDF-fs: warning (device md0): udf_fill_super: No 
partition found (2)
[ 3463.731052] JBD2: Invalid checksum recovering block 630194476 in log
[ 3464.933960] Buffer I/O error on dev md0p1, logical block 630194474, 
lost async page write
[ 3464.933971] Buffer I/O error on dev md0p1, logical block 630194475, 
lost async page write
[ 3465.928066] JBD2: recovery failed
[ 3465.928070] EXT4-fs (md0p1): error loading journal
[ 3465.936852] VFS: Dirty inode writeback failed for block device md0p1 
(err=-5).


Thanks a lot for your time


Joseba Ibarra

Adam Goryachev <mailto:adam@websitemanagers.com.au>
11 de octubre de 2017, 13:29
Hi Rudy,

Please send the output of all of the following commands:

cat /proc/mdstat

mdadm --manage /dev/md0 --stop

mdadm --assemble /dev/md0 /dev/sd[bcd]1

cat /proc/mdstat

mdadm --manage /dev/md0 --run

mdadm --manage /dev/md0 --readwrite

cat /proc/mdstat


Basically the above is just looking at what the system has done 
currently, stopping/clearing that, and then trying to assemble it 
again, finally, we try to start it, even if it has one faulty disk.

At this stage, chances look good for recovering all your data, though 
I would advise to get yourself a replacement disk for the dead one so 
that you can restore redundancy as soon as possible.

Regards,Adam