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Thread: RAID starting at md127 instead of md0

  1. #21
    Join Date
    Oct 2009
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    2,199
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    Ubuntu 10.10 Maverick Meerkat

    Re: RAID starting at md127 instead of md0

    Quote Originally Posted by CrazyMike View Post
    OK, nevermind /dev/md0p1 appears to be normal partition naming, so it appears I'm in good shape here...
    Sort of normal. mdadm can create sub-partitions within a single md device. I have never used this "feature" and my brief experiments failed when trying to use normal tools to recognize the sub partitions. Anyhow, the naming style "mdxpy" is used to denote partition y of array x.

    BTW when I want to have multiple partitions on a single md device I use LVM. Some folks avoid the issue by creating separate md devices for each partition they need.
    ASRock P67 Extreme6, Intel i5 2500K, 8GB RAM, nVidia 6600GT, 4x1TB RAID1+0

  2. #22
    Join Date
    Jul 2008
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    Re: RAID starting at md127 instead of md0

    Quote Originally Posted by dougnaka View Post
    FYI, if you are trying to use a large drive (2TB in my case) your problem is not simply mis-numbered RAID devices, it's the partition table on large drives are not the same. You have to use a GUID partition table (GPT) instead of the legacy MBR in all drives larger than 2TB.
    Google "GUID partition table (GPT) grub linux howto"

    When I create a new md# of a GPT partition on 12.04 LTS I do not have an "ARRAY" entry in /etc/mdadm/mdadm.conf for that md# auto-generated for me.

    If I run
    Code:
    sudo mdadm --detail --scan
    the output line for "md127" is

    ARRAY /dev/md/myhostname:2 metadata=1.2 name=myhostname:2 UUID=xx77xxf7:xx53xx89:acxxa4xx:xx33xxf9

    but when I put

    ARRAY /dev/md2 metadata=1.2 UUID=xx77xxf7:xx53xx89:acxxa4xx:xx33xxf9

    into /etc/mdadm/mdadm.conf the array still comes up as md127

    If I go to the trouble of using
    Code:
    mdadm --stop /dev/md127
    mdadm --assemble /dev/md2 /dev/sdc1 /dev/sdd1
    before running the mdscan I still get:

    ARRAY /dev/md2 metadata=1.2 name=myhostname:2 UUID=xx77xxf7:xx53xx89:acxxa4xx:xx33xxf9

    Which doesn't help me a bit.
    Last edited by nutznboltz; January 19th, 2012 at 03:19 PM.

  3. #23
    Join Date
    Jun 2007
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    3

    Re: RAID starting at md127 instead of md0

    I suspect this is mostly related to the default device mapping changing from /dev/sdXX to /dev/xvdXXX

    See my write up on page 5 over here:
    http://ubuntuforums.org/showthread.php?t=1468064&page=5

    simply try changing the device line in mdadm.conf, adjust for your devices obviously:

    #DEVICE /dev/sdh[1-8]
    DEVICE /dev/xvdh[1-8]

    As I say in the other thread - I pulled my hair out today on this one and I think the device naming problem makes some sense. AS soon as I fed mdadm the correct device names all my problems cleared up - and the default output of mdadm --detail --scan works fine in mdadm.conf

  4. #24
    Join Date
    May 2008
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    Ubuntu

    Re: RAID starting at md127 instead of md0

    Thanks , yes we can. That solved my problem as well.

  5. #25
    Join Date
    Jan 2013
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    6

    Re: RAID starting at md127 instead of md0

    Quote Originally Posted by YesWeCan View Post
    Hi all.
    This seems to be a "feature" of the mdadm in the newest kernel.
    [...]
    So I would try minimizing the specifiers in your ARRAY statements: all you normally need is device name and UUID:
    Code:
    ARRAY /dev/md0 UUID=e4665ceb:15f8e4b6:b186d497:7d365254
    And there seems to be some change to do with /dev/md/* and /dev/md* which I don't yet understand.

    2) You need to update initramfs so it contains your mdadm.conf settings during boot.
    Code:
    sudo update-initramfs -u
    Try those and report back.
    I was tearing my hair out on this one. Was migrating a RAID 1 array from a 10.04 box in which the system drive failed, so didn't have access to its mdadm.conf file. mdadm in 12.04 seems to "find" the array a little more easily than 10.04, but was also getting the md127 ("foreign") array crap happening.
    What I did:
    Note: The following was all done logged in as root.

    1) Get device names for array:
    Code:
    fdisk -l
    2) In my case, my RAID 1 devices are sdb1 and sdc1, so I ran:
    Code:
    mdadm --assemble /dev/md0 /dev/sdb1 /dev/sdc1
    mdadm --detail --scan
    3) Output from scan - with extraneous info removed - was used to update /etc/mdadm/mdadm.conf:
    Code:
    ARRAY /dev/md0 UUID=af4*****:d39*****:998*****:82e*****
    4) Then I ran:
    Code:
    update-initramfs -u
    and rebooted.
    Problem solved.

    Thanks, YesWeCan!
    Dirk

  6. #26
    Join Date
    Jan 2010
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    Holland
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    Distro
    Kubuntu 10.04 Lucid Lynx

    Re: RAID starting at md127 instead of md0

    Create !!!

    Got it working too.

    Thanks.

  7. #27
    Join Date
    Oct 2006
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    Ayrshire
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    Ubuntu Development Release

    Re: RAID starting at md127 instead of md0

    Old thread closed.

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