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I was asked by a friend if I am able to recover a crashed volume on a Synology DS207+, that was set up with a JBOD volume of 2 disks.

At some point the system crashed (probably a power outage) and it is left with a crashed volume.

It seems the volume 1 has forgotten about DISK 1 and is only showing DISK 2.

Looking at the disks themselves both are listed as working normally but DISK 1 is not initialized while disk 2 still belongs to Volume 1.

The disks are both identical 2 TB hard disks.

I have taken out both disks and ran a surface scan to rule out any faulty disks. Both disks came out clean with no bad sectors, which is why I have hope that maybe the volume can be simply put together again with no data loss.

I hooked the disks back up and SSH'd into the system to get to know more about the volume.

fdisk -l:

Disk /dev/sda: 2000.3 GB, 2000398934016 bytes
255 heads, 63 sectors/track, 243201 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Device Boot      Start         End      Blocks  Id System
/dev/sda1               1         311     2490240  fd Linux raid autodetect
Partition 1 does not end on cylinder boundary
/dev/sda2             311         572     2097152  fd Linux raid autodetect
Partition 2 does not end on cylinder boundary
/dev/sda3             588      243201  1948793440+ fd Linux raid autodetect

Disk /dev/sdb: 2000.3 GB, 2000398934016 bytes
255 heads, 63 sectors/track, 243201 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Device Boot      Start         End      Blocks  Id System
/dev/sdb1               1         311     2490240  fd Linux raid autodetect
Partition 1 does not end on cylinder boundary
/dev/sdb2             311         572     2097152  fd Linux raid autodetect
Partition 2 does not end on cylinder boundary
/dev/sdb3             588      243201  1948793440+ fd Linux raid autodetect

cat /proc/mdstat:

Personalities : [linear] [raid0] [raid1] [raid10] [raid6] [raid5] [raid4]
md2 : active linear sdb3[1]
      1948793408 blocks super 1.1 64k rounding [2/1] [_U]

md1 : active raid1 sdb2[1]
      2097088 blocks [2/1] [_U]

md0 : active raid1 sdb1[1]
      2490176 blocks [2/1] [_U]

unused devices: <none>

Looks like there were multiple setups at some point. I looked into /etc/fstab to see what was currently set up:

/dev/root / ext3 defaults 1 1
none /proc proc defaults 0 0
/dev/md2 /volume1 ext3 defaults 0 0

So md2 is the active setup. I took a closer look at it.

mdadm --detail /dev/md2:

/dev/md2:
        Version : 01.01
  Creation Time : Thu Feb 17 12:49:46 2011
     Raid Level : linear
     Array Size : 1948793408 (1858.51 GiB 1995.56 GB)
   Raid Devices : 2
  Total Devices : 1
Preferred Minor : 2
    Persistence : Superblock is persistent

    Update Time : Sun Mar 10 11:36:50 2019
          State : active, degraded
 Active Devices : 1
Working Devices : 1
 Failed Devices : 0
  Spare Devices : 0

       Rounding : 64K

           Name : 2
           UUID : 763a5c64:fbc0e3f6:fb3c451b:521efa98
         Events : 7

    Number   Major   Minor   RaidDevice State
       0       0        0        0      removed
       1       8       19        1      active sync   /dev/sdb3

Now I am getting into unfamiliar territory because I have never set up raids by hand before and I am unfamiliar with all that mdadm can do. I attempted to simply add the disk to the volume but that will not work.

mdadm --manage /dev/md2 --add /dev/sda3:

mdadm: add new device failed for /dev/sda3 as 2: Invalid argument

And the same with --re-add instead of --add.

I am now a tad afraid to proceed with any other commands when looking for similar issues and their solutions as I do not want to erase the data. Of course if there is no other way when I want to get the disks into a working order again then that is that. I know that JBODs are not the way to go without any additional means of backing up the data and my friend obviously does so now as well. :)

But it would still be great if I could somehow rescue this whole mess and in future set it up in a proper manner.

Edit:

Alternatively, if the data on both disks can be rescued outside of the Synology Diskstation, this would be a valid solution as well. I have a spare 4 TB disk which could fit the data of the 2 2 TB disks. Can the data of the linux raid autodetect partitions simply be read and copied to the bigger disk?

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