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Thread: mdadm raid 5 help - new raid degraded

  1. #1
    Join Date
    Oct 2008

    mdadm raid 5 help - new raid degraded

    I've setup a few raids on ubuntu before without issue. I'm trying to spin up a quick one with two new 2TB drives on a raid 5 on ubunbu 13.10

    I ran badblocks on both drives to see if they were ok:

    Checking blocks 0 to 1953513542
    Checking for bad blocks (read-only test): done  
    Pass completed, 0 bad blocks found. (0/0/0 errors)
    I tried ext4 and xfs filesytems

    Here is how i assembled the raid which worked without error:

    sudo mdadm --create --verbose /dev/md0 --level=5 --raid-devices=2 /dev/sda1 /dev/sdb1
    i was able to format /dev/md0

    when i reboot, i'm alerted that the raid is degraded and dropped to a initramfs rescue prompt.

    The only difference today is that these new drives needed their partitions created with gdisk instead of fdisk because fdisk reported:

    Warning: invalid flag 0x0000 of partition table 4 will be corrected by w(rite)

    The device presents a logical sector size that is smaller than
    the physical sector size. Aligning to a physical sector (or optimal
    I/O) size boundary is recommended, or performance may be impacted.
    which i'm lead to believe means that fdisk on ubuntu 13.10 doesn't understand a new standard in large drives with a large block size (or something) gdisk seemed to handle it ok.

    any advice would be appreciated.

  2. #2
    Join Date
    Sep 2008
    Ubuntu 12.04 Precise Pangolin

    Re: mdadm raid 5 help - new raid degraded

    The minimum for non-degraded RAID5 is 3 disks.

    You probably have 4k sector disks.

    Use this command to check if the 4k align is setup correctly:
    parted /dev/sda align-check m 1
    m = minimal, checks for 4k alignment.
    o = optimal, checks for 1M alignment.

    1 = partition number on device.

  3. #3
    Join Date
    Oct 2008

    Re: mdadm raid 5 help - new raid degraded

    thanks a bunch, i didn't know about the disk limit but it makes perfect sense. reduced my raid level and things are just fine.

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