Synology NAS having degraded RAID

We recently started monitoring our Synology NAS with CloudRadar.io (monitoring software) and we were getting the following alert…

Module software raid health according to /proc/mdstat has alert(s)

Raid md0 degraded. Missing 5 devices. Raid md0 degraded. Missing 5 devices. Raid status not optimal (Needs Attention)

Raid md1 degraded. Missing 5 devices. Raid md0 degraded. Missing 5 devices. Raid status not optimal (Needs Attention)

After SSHing into the NAS and running cat /proc/mdstat I noticed MD0 and MD1 had missing disks. Those arrays are were not created by me. They appear to come from the factory and contain recovery data for the NAS.

synology_nas:/$ cat /proc/mdstat
Personalities : [linear] [raid0] [raid1] [raid10] [raid6] [raid5] [raid4] [raidF1] 
md2 : active raid5 sda3[0] sdi3[6] sdg3[5] sdf3[4] sde3[3] sdc3[2] sdb3[1]
      46855227264 blocks super 1.2 level 5, 64k chunk, algorithm 2 [7/7] [UUUUUUU]
      
md1 : active raid1 sda2[0] sdb2[1] sdc2[2] sde2[3] sdf2[4] sdg2[5] sdi2[6]
      2097088 blocks [12/7] [UUUUUUU_____]
      
md0 : active raid1 sda1[0] sdb1[1] sdc1[2] sde1[3] sdf1[4] sdg1[5] sdi1[6]
      2490176 blocks [12/7] [UUUUUUU_____]

Looking further into the array I ran mdadm –detail /dev/md0

synology_nas:/$ sudo mdadm --detail /dev/md0
/dev/md0:
        Version : 0.90
  Creation Time : Wed Feb  7 16:33:01 2018
     Raid Level : raid1
     Array Size : 2490176 (2.37 GiB 2.55 GB)
  Used Dev Size : 2490176 (2.37 GiB 2.55 GB)
   Raid Devices : 12
  Total Devices : 7
Preferred Minor : 0
    Persistence : Superblock is persistent

    Update Time : Tue Jun  9 09:22:20 2020
          State : clean, degraded 
 Active Devices : 7
Working Devices : 7
 Failed Devices : 0
  Spare Devices : 0

           UUID : 0386309b:f65fbf8a:c69de3af:22ddbed7
         Events : 0.36734185

    Number   Major   Minor   RaidDevice State
       0       8        1        0      active sync   /dev/sda1
       1       8       17        1      active sync   /dev/sdb1
       2       8       33        2      active sync   /dev/sdc1
       3       8       65        3      active sync   /dev/sde1
       4       8       81        4      active sync   /dev/sdf1
       5       8       97        5      active sync   /dev/sdg1
       6       8      129        6      active sync   /dev/sdi1
       -       0        0        7      removed
       -       0        0        8      removed
       -       0        0        9      removed
       -       0        0       10      removed
       -       0        0       11      removed

The reason for the error is both arrays report status: clean, degraded due to having 12 disks out of the 7 installed. I went ahead and set MD0 and MD1 to 7 disks using mdadm –grow -n 7 /dev/mdx

synology_nas:/$ sudo mdadm --grow -n 7 /dev/md0
synology_nas:/$ sudo mdadm --grow -n 7 /dev/md1

synology_nas:/$ sudo mdadm --detail /dev/md0
/dev/md0:
        Version : 0.90
  Creation Time : Wed Feb  7 16:33:01 2018
     Raid Level : raid1
     Array Size : 2490176 (2.37 GiB 2.55 GB)
  Used Dev Size : 2490176 (2.37 GiB 2.55 GB)
   Raid Devices : 7
  Total Devices : 7
Preferred Minor : 0
    Persistence : Superblock is persistent

    Update Time : Tue Jun  9 09:33:38 2020
          State : clean 
 Active Devices : 7
Working Devices : 7
 Failed Devices : 0
  Spare Devices : 0

           UUID : 0386309b:f65fbf8a:c69de3af:22ddbed7
         Events : 0.36734590

    Number   Major   Minor   RaidDevice State
       0       8        1        0      active sync   /dev/sda1
       1       8       17        1      active sync   /dev/sdb1
       2       8       33        2      active sync   /dev/sdc1
       3       8       65        3      active sync   /dev/sde1
       4       8       81        4      active sync   /dev/sdf1
       5       8       97        5      active sync   /dev/sdg1
       6       8      129        6      active sync   /dev/sdi1

They now show their status as clean and we no longer receive any alerts from our device monitoring system!

I was able to figure this out due to a number of sites / articles which I’ll list below…

• https://blog.sdbarker.com/post/synology-nas-ds1813-degraded-array-for-md0-and-md1-after-rebuild/
• https://support.unitrends.com/UnitrendsBackup/s/article/000002500
• https://www.digitalocean.com/community/tutorials/how-to-manage-raid-arrays-with-mdadm-on-ubuntu-16-04#:~:text=If%20you%20look%20at%20the,md0%20%2D%2Dremove%20%2Fdev%2Fsdc