Strange behaviour after 'dd' - Unix

This is a discussion on Strange behaviour after 'dd' - Unix ; Hi people. A 5GB disk started failing and before (I hoped) disaster, I did a 'dd' of each partition to a new (larger) disk. It went fairly well, but after doing it I find strange results: 1) df reports the ...

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  1. Strange behaviour after 'dd'

    Hi people.

    A 5GB disk started failing and before (I hoped) disaster, I did a 'dd'
    of each partition
    to a new (larger) disk. It went fairly well, but after doing it I find
    strange results:

    1) df reports the original sizes:

    Filesystem 1K-blocks Used Available Use% Mounted on
    /dev/hda1 2270080 1857408 295496 87% /
    /dev/hda3 2365300 352328 1890880 16% /usr/local

    2.27 + 2.36 + a swap partition is the original 5 GB drive. On this
    one, there is
    10 GB available, and the first partition is 4 GB (not 2.27).

    2) fdisk reports correctly:

    Device Boot Start End Blocks Id System
    /dev/hda1 * 1 479 3846260 83 Linux
    /dev/hda2 488 498 88357+ 82 Linux swap
    /dev/hda3 499 1245 6000277+ 83 Linux

    3) parted also reports correctly:

    Minor Start End Type Filesystem Flags
    1 0.031 3756.144 primary ext3 boot
    2 3820.144 3906.430 primary linux-swap
    3 3906.431 9766.076 primary ext3

    4) gparted reports the above (parted's) partitions, but seems to
    _scale_ the
    usage of 'df' and reports

    3.27 GB used of 3.67 GB on hda1
    3.80 GB used of 5.72 GB on hda3

    This simple can't be - 3.27 + 3.80 is larger than the original disk
    where I
    copied from!

    What did I do wrong, and can I fix this?

    Thanks in advance!


  2. Re: Strange behaviour after 'dd'

    Begin <1169939445.473733.125610@a34g2000cwb.googlegroups. com>
    On 2007-01-27, john.coppens@gmail.com wrote:
    > A 5GB disk started failing and before (I hoped) disaster, I did a 'dd'
    > of each partition to a new (larger) disk. It went fairly well, but
    > after doing it I find strange results:

    [snip!]
    >
    > What did I do wrong, and can I fix this?


    You copied the entire filesystem down to its layout, so for all *it*
    knows, it is still the previous size. The simple way to fix it is to not
    try a bitwise copy like you did with dd, but to create the filesystem(s)
    to the right sizes then use a filesystem level tool such as dump/restore
    or an archiver (eg tar[1]) to transfer the data and associated metadata.


    [1] Be aware of the limitations of the particular tar you're using;
    star is a good tar implementation with lots of options.

    --
    j p d (at) d s b (dot) t u d e l f t (dot) n l .
    This message was originally posted on Usenet in plain text.
    Any other representation, additions, or changes do not have my
    consent and may be a violation of international copyright law.

  3. Re: Strange behaviour after 'dd'

    On 27 Jan 2007 15:10:45 -0800, john.coppens@gmail.com wrote:

    >Hi people.
    >
    >A 5GB disk started failing and before (I hoped) disaster, I did a 'dd'
    >of each partition
    >to a new (larger) disk. It went fairly well, but after doing it I find
    >strange results:
    >
    >1) df reports the original sizes:


    >
    >This simple can't be - 3.27 + 3.80 is larger than the original disk
    >where I
    >copied from!
    >
    >What did I do wrong, and can I fix this?
    >
    >Thanks in advance!


    Only use dd to copy from partitions of the exact same size.
    Use cpio instead, google for "cpio backup"

    zentara

    --
    I'm not really a human, but I play one on earth.
    http://zentara.net/japh.html

  4. Re: Strange behaviour after 'dd'

    You copied the entire filesystem down to its layout, so for all *it*
    > knows, it is still the previous size. The simple way to fix it is to not
    > try a bitwise copy like you did with dd, but to create the filesystem(s)
    > to the right sizes then use a filesystem level tool such as dump/restore
    > or an archiver (eg tar[1]) to transfer the data and associated metadata.
    >
    > [1] Be aware of the limitations of the particular tar you're using;
    > star is a good tar implementation with lots of options.


    Thanks - I did suspect as much. But I don't think I can access the
    original disk anymore
    now. It was already making strange noises, and I did the 'dd' as sort
    of panic reaction.

    Can I adjust the size of the copied image to the actual size of the
    new partition
    somehow?

    John


  5. Re: Strange behaviour after 'dd'

    Begin <1169992981.665221.133970@l53g2000cwa.googlegroups. com>
    On 2007-01-28, john.coppens@gmail.com wrote:
    [please do include attribution when quoting]
    > Thanks - I did suspect as much. But I don't think I can access the
    > original disk anymore now. It was already making strange noises, and I
    > did the 'dd' as sort of panic reaction.


    You could try. And, of course, `backups'.


    > Can I adjust the size of the copied image to the actual size of the
    > new partition somehow?


    Well, you could try and take a dump off the copy, then restore it after
    you've set the disk up differently. Or you could venture to use tools
    like `growfs', altough those are system dependent. As always, taking
    backups before trying stuff like that is a good precaution.


    --
    j p d (at) d s b (dot) t u d e l f t (dot) n l .
    This message was originally posted on Usenet in plain text.
    Any other representation, additions, or changes do not have my
    consent and may be a violation of international copyright law.

  6. Re: Strange behaviour after 'dd'


    > Or you could venture to use tools
    > like `growfs', altough those are system dependent. As always, taking
    > backups before trying stuff like that is a good precaution.
    >


    Thanks jpd...

    I've just noticed that it may be as simple as running resize2fs, which
    seems just
    the tool I need. I'll try it this a'noon when I go there and can
    unmount the
    drives.

    Groetjes,
    John


  7. Re: Strange behaviour after 'dd'

    john.coppens@gmail.com wrote:
    > A 5GB disk started failing and before (I hoped) disaster, I did a 'dd'
    > of each partition
    > to a new (larger) disk. It went fairly well, but after doing it I find
    > strange results:
    >
    > 1) df reports the original sizes:
    >
    > Filesystem 1K-blocks Used Available Use% Mounted on
    > /dev/hda1 2270080 1857408 295496 87% /
    > /dev/hda3 2365300 352328 1890880 16% /usr/local
    >
    > 2.27 + 2.36 + a swap partition is the original 5 GB drive. On this
    > one, there is
    > 10 GB available, and the first partition is 4 GB (not 2.27).
    >
    > 2) fdisk reports correctly:
    >
    > Device Boot Start End Blocks Id System
    > /dev/hda1 * 1 479 3846260 83 Linux
    > /dev/hda2 488 498 88357+ 82 Linux swap
    > /dev/hda3 499 1245 6000277+ 83 Linux
    >
    > What did I do wrong, and can I fix this?


    Nothing all that incredibly "strange" here. You copied the
    filesystems with dd, so as long as the target partitions aren't
    smaller than the originals, and are set to the same partition type,
    and the source filesystems were unmounted or mounted read-only when
    you copied them, you should be in pretty good shape.

    Copying a filesystem - e.g. with dd - doesn't grow it, so if the
    target partition is larger, the filesystem doesn't automagically grow
    to fill the partition. You can grow the filesystem when it's
    unmounted (e.g. with resize2fs) or with ext2online while it's mounted.


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