I am running OMV 3.0.99 on my NAS. I have set up a RAID5 (with mdadm) containing of three 5TB WD RED drives. I have set up the RAID using the OMV GUI back in the day (2016).

Recently one of the disks has failed (Used to be /dev/sdd). When I got home I ve noticed that it makes weird sounds when starting and that it was not recognized anymore in LINUX. The device seems to be physically broken and I have set up a RMA since I still have warranty on the drives. Now I am waiting for the replacement drive and asking myself what I should do when the new drive is here to recover my RAID.

Some notes on my drives:

  1. /dev/sda is my system drive
  2. the RAID contained of disks /dev/sdb, sdc and sdd. The drive /dev/sdd failed and has been physically removed from the NAS case.
  3. Now /dev/sdd was assigned to my backup disk (used to be sde before the RAID disk failed)

Here are some important outputs of my system:

uname -a output

Linux homenas 4.9.0-0.bpo.6-amd64 #1 SMP Debian 4.9.88-1+deb9u1~bpo8+1 (2018-05-13) x86_64 GNU/Linux

cat /proc/mdstat:

Personalities : [raid6] [raid5] [raid4] 
md127 : active raid5 sdb[0] sdc[1]
        9767278592 blocks super 1.2 level 5, 512k chunk, algorithm 2 [3/2] [UU_]
unused devices: <none>


/dev/sda1: UUID="911053a9-f06c-4479-becb-cb8faa2a5783" TYPE="ext4" PARTUUID="2c92f843-01"
/dev/sda5: UUID="28ae7474-1d14-48a6-9e8e-2ed31e060803" TYPE="swap" PARTUUID="2c92f843-05"
/dev/sdb: UUID="bb8b3798-d160-71b4-cc60-bc8fdc8e0761" UUID_SUB="e52bb12c-23e1-7c8f-a7f7-d52d4b2b46a9" LABEL="HomeNAS:NAS" TYPE="linux_raid_member"
/dev/sdc: UUID="bb8b3798-d160-71b4-cc60-bc8fdc8e0761" UUID_SUB="d9eac207-7167-d19e-c1de-8c7525b77d48" LABEL="HomeNAS:NAS" TYPE="linux_raid_member"
/dev/sdd1: UUID="523cffe7-115d-49b4-95e0-7549aecdf064" TYPE="ext4" PARTUUID="fba4a7ee-026a-497f-9b3d-bbdec92cb0d6"
/dev/md127: UUID="bd5ef96f-5587-4211-95c0-10219985ff6d" TYPE="ext4"

fdisk -l | grep "Disk ":

Disk /dev/sda: 29,8 GiB, 32017047552 bytes, 62533296 sectors
Disk identifier: 0x2c92f843
Disk /dev/sdb: 4,6 TiB, 5000981078016 bytes, 9767541168 sectors
Disk /dev/sdc: 4,6 TiB, 5000981078016 bytes, 9767541168 sectors
Disk /dev/sdd: 1,8 TiB, 2000394706432 bytes, 3907020911 sectors
Disk identifier: C0401C51-A74A-4675-935E-AF9BF6706166
Disk /dev/md127: 9,1 TiB, 10001693278208 bytes, 19534557184 sectors

cat /etc/mdadm/mdadm.conf:

# mdadm.conf
# Please refer to mdadm.conf(5) for information about this file.
# by default, scan all partitions (/proc/partitions) for MD superblocks.
# alternatively, specify devices to scan, using wildcards if desired.
# Note, if no DEVICE line is present, then "DEVICE partitions" is assumed.
# To avoid the auto-assembly of RAID devices a pattern that CAN'T match is
# used if no RAID devices are configured.
DEVICE partitions

# auto-create devices with Debian standard permissions
CREATE owner=root group=disk mode=0660 auto=yes

# automatically tag new arrays as belonging to the local system
HOMEHOST <system>

# definitions of existing MD arrays
ARRAY /dev/md/NAS metadata=1.2 name=HomeNAS:NAS UUID=bb8b3798:d16071b4:cc60bc8f:dc8e0761
# instruct the monitoring daemon where to send mail alerts

mdadm --detail --scan --verbose:

ARRAY /dev/md127 level=raid5 num-devices=3 metadata=1.2 name=HomeNAS:NAS UUID=bb8b3798:d16071b4:cc60bc8f:dc8e0761

mdadm --detail /dev/md127:

          Version : 1.2
Creation Time : Sat Mar 12 17:22:49 2016
       Raid Level : raid5
       Array Size : 9767278592 (9314.80 GiB 10001.69 GB)
  Used Dev Size : 4883639296 (4657.40 GiB 5000.85 GB)
   Raid Devices : 3
  Total Devices : 2
    Persistence : Superblock is persistent
            Update Time : Sun Jan 27 13:11:42 2019
                  State : clean, degraded 
         Active Devices : 2
        Working Devices : 2
         Failed Devices : 0
          Spare Devices : 0
                 Layout : left-symmetric
             Chunk Size : 512K
                   Name : HomeNAS:NAS
                   UUID : bb8b3798:d16071b4:cc60bc8f:dc8e0761
                 Events : 305
            Number   Major   Minor   RaidDevice State
               0       8       16        0      active sync   /dev/sdb
               1       8       32        1      active sync   /dev/sdc
               4       0        0        4      removed

I have searched the internet and found different steps, but I dont know which are necessary in my situation:

  1. mark disk as failed
  2. remove disk from array
  3. copy partition table of one remaining disk of the array to the new replacement drive
  4. re-add drive to the array (--> rebuild will be automatically be initiated)

Since the disk failed completly and was not present in Linux anymore I could not mark it as failed and remove it from the array. I have found the following command to remove a disk from the array which is not present anymore: mdadm /dev/md127 -r detached

Is it recommended to use this command before I install the new drive? Or is it not necessary to remove the drive from the array in my case?

I would really appreciate your guidance! Thanks in advance

  • 1
    Please review the formatting help to learn about how to properly format text on Stack Exchange sites. – Daniel B Jan 29 at 9:51
  • 1
    You should.nit be using RAID5 with 9tb of disk - the chances of a second failure during rebuild is to high. Vonsider in the future converting to RAID10 – davidgo Jan 29 at 18:55

Basically it's just a simple

mdadm /dev/md127 --add /dev/newdrive

and then watch cat /proc/mdstat and/or dmesg -w for rebuild progress or failure.

The sooner you add a new drive to the array, the better. If another drive fails while you wait, that's it. If you don't have a backup of your data, make one ASAP.

Normally you'd also create a partition table on the drive first and then use the partition for the RAID, and not the drive directly. But it's not possible in your case since you already have unpartitioned drives in your array, and adding a partition table now, the size would no longer match.

Running drives without partition table is a potential cause for data loss. Too much software out there that helpfully creates a partition table for you if it doesn't see one, also easy to accidentally do it yourself.

  • Thank you for your answer. I have shutdown the NAS until I have the replacement drive. I have a Backup of my important data. What about the RaidDevice 4 that is shown as „removed“? Dont I have to remove it from the array before adding a new disk? – bash0r1988 Jan 29 at 11:52

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