I am hopefull!

After spending some time reading, poking around in the Synology Community Forum, I extended my search for information on how to recover a RAID volume to more general Linux resources. As it turns out this seems to be the way to go, because Synology’s DSM is build on top of Linux; hence in case you want to get your hand dirty, the literature to consult is that for Linux System Administrators.

Consulting the information recorded in /var/log/, /etc/space/space_history* and /etc/lvm/archive I have been trying to piece together the input for starting the reassembly of the lost volume. Since adding all the drives at the same would fail I have been splitting the operation into two parts:

  • Assemble volume:

     mdadm --verbose -Af /dev/md4 /dev/sd[abcdefghijk]7
    
  • Add missing device:

     mdadm --manage /dev/md4 --add /dev/sdl7
    

If I now check via

cat /proc/mdstat

I indeed can see that there is an ongoing recovery:

Personalities : [linear] [raid0] [raid1] [raid10] [raid6] [raid5] [raid4]
md4 : active raid5 sdl7[12] sdd7[0] sdk7[11] sdj7[10] sdc7[9] sdb7[8] sda7[7] sdi7[5] sdh7[4] sdg7[3] sdf7[2] sde7[1]
      5372036032 blocks super 1.2 level 5, 64k chunk, algorithm 2 [12/11] [UUUUUU_UUUUU]
      [=>...................]  recovery =  6.8% (33485312/488366912) finish=276.1min speed=27452K/sec

md5 : active raid5 sdc6[12] sdb6[13] sda6[11] sdk6[10] sdj6[8] sdi6[7] sdg6[5] sdh6[6] sdf6[4] sde6[2] sdd6[1]
      5372034624 blocks super 1.2 level 5, 64k chunk, algorithm 2 [12/11] [UUUUUUU_UUUU]

md3 : active raid5 sdh8[0] sdb8[9] sdc8[8] sda8[7] sdk8[6] sdj8[3] sdi8[2] sdg8[1]
      7813942272 blocks super 1.2 level 5, 64k chunk, algorithm 2 [9/8] [UUU_UUUUU]

md6 : active raid5 sdc9[0] sdb9[1]
      5860301056 blocks super 1.2 level 5, 64k chunk, algorithm 2 [3/2] [UU_]

md1 : active raid1 sda2[0] sdb2[1] sdc2[2] sdd2[3] sde2[4] sdf2[5] sdg2[6] sdh2[7] sdi2[8] sdj2[9] sdk2[10] sdl2[11]
      2097088 blocks [12/12] [UUUUUUUUUUUU]

md0 : active raid1 sda1[1] sdb1[10] sdc1[2] sdd1[5] sde1[7] sdf1[6] sdg1[3] sdh1[4] sdi1[8] sdj1[9] sdk1[0] sdl1[11]
      2490176 blocks [12/12] [UUUUUUUUUUUU]

unused devices: <none>

Of course I would not want to jinx it, but with a bit of luck I might have been able to make some actual process towards the recovery of the system.