how does mdadm know how to reconcile drives? - Setup

This is a discussion on how does mdadm know how to reconcile drives? - Setup ; Dear linux wizards: I had a drive that contained a partition that I wanted to raid-1 with another drive. I backed it up, thinking that raiding it (mdadm --create) would destroy its contents. I used mdadm, and to my amazement, ...

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Thread: how does mdadm know how to reconcile drives?

  1. how does mdadm know how to reconcile drives?


    Dear linux wizards: I had a drive that contained a partition that I
    wanted to raid-1 with another drive. I backed it up, thinking that
    raiding it (mdadm --create) would destroy its contents. I used mdadm,
    and to my amazement, all the content was still there. the partition on
    the other drive had no files on it, I believe, except perhaps
    lost+found.

    so, I am now trying to understand how the magic works. how does mdadm
    reconcile differences in the contents of the two partitions? if I
    asked it to create a raid and the two partitions contain different
    files, do both appear? is it unreliable? what if each is filled 51%
    with totally different files?

    explanations appreciated.

    sincerely,

    /iaw


  2. Re: how does mdadm know how to reconcile drives?

    ivowel@gmail.com wrote:
    > Dear linux wizards: I had a drive that contained a partition that I
    > wanted to raid-1 with another drive. I backed it up, thinking that
    > raiding it (mdadm --create) would destroy its contents. I used mdadm,
    > and to my amazement, all the content was still there. the partition on
    > the other drive had no files on it, I believe, except perhaps
    > lost+found.
    >
    > so, I am now trying to understand how the magic works. how does mdadm
    > reconcile differences in the contents of the two partitions? if I
    > asked it to create a raid and the two partitions contain different
    > files, do both appear? is it unreliable? what if each is filled 51%
    > with totally different files?
    >
    > explanations appreciated.


    The first drive added to an array will be copied to the second drive.
    Ordinarily you should create an array with a missing element to insure
    the "first drive" is the one you want. You just got lucky.

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