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Thread: MDADM RAID rebuilds incorrectly on reboot

  1. #1
    Join Date
    Jul 2007
    Toronto, Ontario, Canada

    MDADM RAID rebuilds incorrectly on reboot

    So my computer has four 1.5 TB drives installed. Up until recently, these drives existed in two RAID1 configurations of 3 TB.

    Recently I decided to create one large RAID5 device out of them instead. I did this remotely, and had no spare drive to dump data to - so I disassembled one of the RAIDs (it was just a backup of the other from a few weeks back) and since the RAID contained under 1.5 TB of data - I created a partition on one of the disks and stored it there.

    So I created the RAID5 in a degraded mode with only 3 disks and copied the data back on to the new 4.5 TB RAID. After that, I added in the remaining disk that had been holding the data throughout the backup process to the RAID and let it rebuild over a few hours.

    This is what the configuration looked like:

    [root@FILEMASTER administrator]# cat /proc/mdstat
    Personalities : [raid6] [raid5] [raid4]
    md0 : active raid5 sdb1[0] sdd1[4] sde1[2] sdc1[1]
          4395016704 blocks super 1.2 level 5, 512k chunk, algorithm 2 [4/4] [UUUU]
    unused devices: <none>
    So I updated my mdadm.conf file and rebooted. Now it appears the disks assemble incorrectly on reboot...

    [root@FILEMASTER administrator]# cat /proc/mdstat
    Personalities :
    md0 : inactive sde1[2](S) sdb1[0](S) sdc1[1](S)
          4395018240 blocks super 1.2
    md127 : inactive sdd[0](S)
          1465138496 blocks
    I can fix it by simply dismantling the md0 and md127 arrays and then running
    mdadm --assemble --scan
    Obviously though, this is inconvenient - and I would prefer the RAID be built properly at boot.

    Anyone have any insight on how I would fix this?


    P.S. /dev/sdd was the 'spare' disk I added after.

  2. #2
    Join Date
    Jul 2010
    Michigan, USA
    Ubuntu 14.04 Trusty Tahr

    Re: MDADM RAID rebuilds incorrectly on reboot

    You need to update your your mdadm.conf file after you make changes like this. Once you have your array running properly just run these steps.

    sudo -i
    echo "DEVICE partitions" > /etc/mdadm/mdadm.conf
    echo "HOMEHOST fileserver" >> /etc/mdadm/mdadm.conf
    echo "MAILADDR" >> /etc/mdadm/mdadm.conf
    mdadm --detail --scan >> /etc/mdadm/mdadm.conf
    update-initramfs -u
    This will update your mdadm.conf file to reflect your RAID5 array and will update the initramfs. This should allow your array to survive a reboot.


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