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I have an Ubuntu 18.04 server with two 1Tb drives in a software RAID1 array, configured during the OS installation process. I wanted the check the health of the array and disks this evening and am not sure if there is a problem with one of my drives.

I see in the 'mdadm --detail /dev/md0' output that one of the drives appears to be removed, and I see from another askubuntu question that the [_U] in the 'cat /proc/mdstat' command output is possibly a signal that a partition has failed.

From the results below, has a drive failed? If so, what is the best course of action? Also, how do I set it so it emails me when a drive fails?

sudo fdisk -l

Disk /dev/loop0: 99.2 MiB, 104030208 bytes, 203184 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes


Disk /dev/loop2: 99.2 MiB, 104026112 bytes, 203176 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes


Disk /dev/sda: 931.5 GiB, 1000204886016 bytes, 1953525168 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: gpt
Disk identifier: 310AB5A9-6622-49D9-82C3-B1F2E53DD560

Device       Start        End    Sectors   Size Type
/dev/sda1     2048    2099199    2097152     1G Linux filesystem
/dev/sda2  2099200 1953521663 1951422464 930.5G Linux filesystem


Disk /dev/sdb: 931.5 GiB, 1000204886016 bytes, 1953525168 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: gpt
Disk identifier: D634E279-44CC-4ED5-B380-07D02C3C3601

Device       Start        End    Sectors   Size Type
/dev/sdb1     2048       4095       2048     1M BIOS boot
/dev/sdb2     4096    2101247    2097152     1G Linux filesystem
/dev/sdb3  2101248 1953521663 1951420416 930.5G Linux filesystem


Disk /dev/md0: 930.4 GiB, 998991986688 bytes, 1951156224 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes

lsblk

NAME    MAJ:MIN RM   SIZE RO TYPE  MOUNTPOINT
loop0     7:0    0  99.2M  1 loop  /snap/core/10908
loop2     7:2    0  99.2M  1 loop  /snap/core/10859
sda       8:0    0 931.5G  0 disk
├─sda1    8:1    0     1G  0 part
└─sda2    8:2    0 930.5G  0 part
sdb       8:16   0 931.5G  0 disk
├─sdb1    8:17   0     1M  0 part
├─sdb2    8:18   0     1G  0 part  /boot
└─sdb3    8:19   0 930.5G  0 part
  └─md0   9:0    0 930.4G  0 raid1 /

cat /etc/mdadm/mdadm.conf

ARRAY /dev/md0 metadata=1.2 name=ubuntu-server:0 UUID=1d9d79bd:d675f751:144db975:0d24caa9
MAILADDR root

sudo mdadm --detail /dev/md0

/dev/md0:
           Version : 1.2
     Creation Time : Fri Aug 30 21:55:50 2019
        Raid Level : raid1
        Array Size : 975578112 (930.38 GiB 998.99 GB)
     Used Dev Size : 975578112 (930.38 GiB 998.99 GB)
      Raid Devices : 2
     Total Devices : 1
       Persistence : Superblock is persistent

     Intent Bitmap : Internal

       Update Time : Sat Apr  3 23:18:52 2021
             State : clean, degraded
    Active Devices : 1
   Working Devices : 1
    Failed Devices : 0
     Spare Devices : 0

Consistency Policy : bitmap

              Name : ubuntu-server:0
              UUID : 1d9d79bd:d675f751:144db975:0d24caa9
            Events : 1907228

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

cat /proc/mdstat

Personalities : [raid1] [linear] [multipath] [raid0] [raid6] [raid5] [raid4] [raid10]
md0 : active raid1 sdb3[1]
      975578112 blocks super 1.2 [2/1] [_U]
      bitmap: 8/8 pages [32KB], 65536KB chunk

unused devices: <none>
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  • Please clarify your OS & release; there was no Ubuntu release in 2018-August (18.08) so you may not be running Ubuntu at all. Please clarify
    – guiverc
    Apr 3, 2021 at 22:52
  • One thing I have discovered with my own server, I have a RAID 5 set up on it and I have had issues with drives going removed or getting errors on them. I replaced all the drive cables with locking SATA cables and have not had any issues since. I can't 100% tell, but it looks as though your sdb3 was in RAID with sda2? If that was the case then it would be just mdadm --manage /dev/md0 --add /dev/sda2 but I am not 100% about that since I did not set up your system but the closest guess I can see with that partition being the closest to sdb3.
    – Terrance
    Apr 3, 2021 at 23:09
  • You can also check your sda drive with a quick sudo smartctl -a /dev/sda | grep overall to show you if the drive PASSED or FAILED.
    – Terrance
    Apr 3, 2021 at 23:27

1 Answer 1

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Thanks Terence. Smartctl showed both disks to be ok so I ran sudo mdadm --manage /dev/md0 --add /dev/sda2 and it went ahead and added the the disk and rebuilt the array. All is looking to be ok again now.

cat /proc/mdstat

Personalities : [raid1] [linear] [multipath] [raid0] [raid6] [raid5] [raid4] [raid10]
md0 : active raid1 sda2[0] sdb3[1]
      975578112 blocks super 1.2 [2/2] [UU]
      bitmap: 2/8 pages [8KB], 65536KB chunk

unused devices: <none>

lsblk

NAME    MAJ:MIN RM   SIZE RO TYPE  MOUNTPOINT
loop0     7:0    0  99.2M  1 loop  /snap/core/10908
loop2     7:2    0  99.2M  1 loop  /snap/core/10859
sda       8:0    0 931.5G  0 disk
├─sda1    8:1    0     1G  0 part
└─sda2    8:2    0 930.5G  0 part
  └─md0   9:0    0 930.4G  0 raid1 /
sdb       8:16   0 931.5G  0 disk
├─sdb1    8:17   0     1M  0 part
├─sdb2    8:18   0     1G  0 part  /boot
└─sdb3    8:19   0 930.5G  0 part
  └─md0   9:0    0 930.4G  0 raid1 /

sudo mdadm --detail /dev/md0

/dev/md0:
           Version : 1.2
     Creation Time : Fri Aug 30 21:55:50 2019
        Raid Level : raid1
        Array Size : 975578112 (930.38 GiB 998.99 GB)
     Used Dev Size : 975578112 (930.38 GiB 998.99 GB)
      Raid Devices : 2
     Total Devices : 2
       Persistence : Superblock is persistent

     Intent Bitmap : Internal

       Update Time : Mon Apr  5 07:46:14 2021
             State : clean
    Active Devices : 2
   Working Devices : 2
    Failed Devices : 0
     Spare Devices : 0

Consistency Policy : bitmap

              Name : ubuntu-server:0
              UUID : 1d9d79bd:d675f751:144db975:0d24caa9
            Events : 1930973

    Number   Major   Minor   RaidDevice State
       0       8        2        0      active sync   /dev/sda2
       1       8       19        1      active sync   /dev/sdb3

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