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Thread: HOWTO: Linux Software Raid using mdadm

  1. #21
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    Aug 2005
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    Re: HOWTO: Linux Software Raid using mdadm

    I am trying to put together a raid1 configuration using two drives one of which is 200g and the other is 250g. I have one using the whole drive ending on cylinder 23241 and then created two partitions on the second, one ending at 23241 also and the other taking up the rest of the drive.

    First off, should I even be trying this with two different drives (the only physical difference according to hdparm is a buffer of 8MB on one and 2MB on t'other)?

    Secondly, and my problem now, is that mdadm stalls at 21.9% and slowly brings the computer to a freeze while doing a resync. Can anyone help me?

  2. #22
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    Re: HOWTO: Linux Software Raid using mdadm

    Next time someone just remind me to check my logs. There must have been 200 read/write errors on one of the drives . . . that'll do it.

  3. #23
    Join Date
    Jun 2007
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    NSW, Australia
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    Kubuntu 7.04 Feisty Fawn

    Re: HOWTO: Linux Software Raid using mdadm

    Quote Originally Posted by mgrusin View Post
    Great howto! Please consider adding this to the community documentaion wiki. There is currently nothing in there (at least that I could find) on the use of mdadm.

    -MG
    There is now i started writing this
    https://help.ubuntu.com/community/In...n/SoftwareRAID

    It's not complete but that's coming

  4. #24
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    Apr 2006
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    Illinois, USA
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    1,283
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    Ubuntu 11.04 Natty Narwhal

    Re: HOWTO: Linux Software Raid using mdadm

    This has helped me more than once. I switched motherboards and didn't realize that it changed hda, etc., to sda, etc., so after a lot of tooling around with it, this guide helped me figure that out!
    If I'm not being clear enough or giving you enough information, just ask

    "But woe to him who is alone when he falls, for he has no one to help him up."

    Smooth scrolling for GTK!

  5. #25
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    Fargo, ND, USA
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    Kubuntu 10.04 Lucid Lynx

    Re: HOWTO: Linux Software Raid using mdadm

    I have software RAID, different levels (0 or 1), on several partitions, one of which is empty. I want to install on the empty one, but I can't see how to do this without nuking the whole array with the installer. If I chroot with the alternate CD, I see my md devices, likewise if I install mdadm on the desktop CD, but neither installer will show the md devices.
    Help yourself: Search the community docs or try other resources.
    Quote Originally Posted by Henry Spencer
    Those who do not understand Unix are condemned to reinvent it, poorly.
    Let science use your computer when you aren't: Folding@Home.

  6. #26
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    Mar 2008
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    Ubuntu 12.04 Precise Pangolin

    Re: HOWTO: Linux Software Raid using mdadm

    I am not sure I understand - do you already have a version of ubuntu installed on partition/s in your box?
    or are you simply booting from live CD and are weary to continue the install to your HD? and are now trying to add the mdadm package at this stage?

    the mdadm you "install" to the desktop Live CD is actually installed to ram as the CD is not altered during the live CD bootup - to create raid devices and mirrors at this stage the alternate install CD is needed

    what I think you are trying to do is install ubuntu from a liveCD and simultaneously maintain the integrity of the other data and OS's on your box by installing ubuntu to a spare partition - being careful - right?
    let us know if this is the case?
    regards
    0,= ,-_-. =.
    ((_/)o o(\_))
    ` `-'(. .)`-'
    000\_/

  7. #27
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    Re: HOWTO: Linux Software Raid using mdadm

    Quote Originally Posted by crtlbreak View Post
    I am not sure I understand - do you already have a version of ubuntu installed on partition/s in your box?
    or are you simply booting from live CD and are weary to continue the install to your HD? and are now trying to add the mdadm package at this stage?

    the mdadm you "install" to the desktop Live CD is actually installed to ram as the CD is not altered during the live CD bootup - to create raid devices and mirrors at this stage the alternate install CD is needed

    what I think you are trying to do is install ubuntu from a liveCD and simultaneously maintain the integrity of the other data and OS's on your box by installing ubuntu to a spare partition - being careful - right?
    let us know if this is the case?
    regards
    Yes, that is exactly what I want to do. I have Ubuntu installed, but I want to do a parallel installation, so I could boot into either. I want to install a separate OS without messing up the current one.

    I understand that when I install mdadm on a live CD, it only exists in RAM. I was just hoping that I could trick the installer into recogizing the md devices.
    Help yourself: Search the community docs or try other resources.
    Quote Originally Posted by Henry Spencer
    Those who do not understand Unix are condemned to reinvent it, poorly.
    Let science use your computer when you aren't: Folding@Home.

  8. #28
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    Mar 2008
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    London
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    Re: HOWTO: Linux Software Raid using mdadm

    grub will manage the separate installations quite fine if they are on different partitions - also not sure if you are installing the same OS version eg 8.04 hardy heron twice but on different partitions - I think that might need a bit more research?
    0,= ,-_-. =.
    ((_/)o o(\_))
    ` `-'(. .)`-'
    000\_/

  9. #29
    Join Date
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    Re: HOWTO: Linux Software Raid using mdadm

    Quote Originally Posted by crtlbreak View Post
    grub will manage the separate installations quite fine if they are on different partitions - also not sure if you are installing the same OS version eg 8.04 hardy heron twice but on different partitions - I think that might need a bit more research?
    I'll deal with grub when I come to that. I'm not at all worried about grub. I put /boot on it's own partition so I can do this sort of thing.

    I want / on a RAID0 device. /boot, /home, and / for the already installed OS are on their own RAID devices (RAID 0 or 1). My roadblock is that the Ubuntu installer will only install to physical partitions (e.g. /dev/sda3) but not general block devices (e.g. /dev/md2), OR it will install to a softraid device but requires destroying the disk. I can't find a workaround, but it seems like a dumb limitation, so I'm hoping there is one.

    I have Hardy installed, and I want to install Gutsy.

    This is for testing the upgrade procedure to Hardy, because I encountered a problem and I want to see if it's repeatable. After coming across this problem, it is now just as much for my own curiosity as it is for investigating the upgrade. I can't understand why such a limitation would be built into the installer. What if I nuked my OS? I would have to nuke my disk (along with my /home) to reinstall with softraid as well?
    Help yourself: Search the community docs or try other resources.
    Quote Originally Posted by Henry Spencer
    Those who do not understand Unix are condemned to reinvent it, poorly.
    Let science use your computer when you aren't: Folding@Home.

  10. #30
    Join Date
    Mar 2008
    Location
    London
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    Ubuntu 12.04 Precise Pangolin

    Re: HOWTO: Linux Software Raid using mdadm

    from the "alternate" installation CD the installer will read your MD devices and you can choose to "do not format the partition" under the installation process. If you are installing on to a newly created partition/LVM/blockdevice then your existing partitions and data integrity should be unaffected if the correct selections have been made under the installation process.

    you are in the classic situation where trying to solve or investigate one issue has created another far greater and more complex issue to try and resolve - how many times have we all been there before??

    a possible suggestion is to use an alternate physical disk rather than mess up your existing system

    I will always apply my five rules
    5 Rules of life
    1. Have you made a backup or can you recover?
    2. If its not broken - try and fix it till its broken as it probably needed replacing anyway
    3. Do not try and destroy one working object in the possibility of repairing another - you will end up with two broken objects.
    4. Paddy's law says that Murphy was an optimist.
    5. No major changes on a Friday - especially after lunchtime

    The rules are best applied in order - I think you are possibly past rule 1 entering in to rule 2?
    0,= ,-_-. =.
    ((_/)o o(\_))
    ` `-'(. .)`-'
    000\_/

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