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    SubjectRe: 2.4.20: ext3/raid5 - allocating block in system zone/multiple 1 requests for sector
    On Sunday March 16, gilbertd@treblig.org wrote:
    > Hi,
    > I've just built an 800GB RAID5 array and built an ext3 file system
    > on it; on trying to copy data off the 200GB RAID it is replacing I'm
    > starting to see errors of the form:
    >
    > kernel: EXT3-fs error (device md(9,2)): ext3_new_block: Allocating block in
    > system zone - block = 140509185
    >
    > and
    >
    > kernel: EXT3-fs error (device md(9,2)): ext3_add_entry: bad entry in
    > directory #70254593: rec_len %% 4 != 0 - offset=28, inode=23880564,
    > rec_len=21587, name_len=76
    >
    > and
    >
    > kernel: raid5: multiple 1 requests for sector 281018464

    I had exactly these symptoms about a year ago in 2.4.18. I found and
    fixed the problem and have just checked and the fix is definately in
    2.4.20.
    So if you really are running 2.4.20 then it looks like a similar bug
    has appeared.

    These two symptoms strongly suggest a buffer aliasing problem.
    i.e. you have two buffers (one for data and one for metadata)
    that refer to the same location on disc.
    One is part of a file that was recently deleted, but the buffer hasn't
    been flushed yet. The other is part of a new directory.
    The old buffer and the new buffer both get written to disc at much the
    same time (hence the "multiple 1 requests"), but the old buffer hits
    the disc second and so corrupts the filesystem.

    The bug I found was specific to data=journal mode, and this certainly
    has more options for buffer aliasing. Were you using data=journal?

    NeilBrown
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