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    SubjectCOW fs (Re: Editing-in-place of a large file)
    Sunday, September 02, 2001, 11:21:37 PM, Bob McElrath wrote:
    BM> I would like to take an extremely large file (multi-gigabyte) and edit
    BM> it by removing a chunk out of the middle. This is easy enough by
    BM> reading in the entire file and spitting it back out again, but it's
    BM> hardly efficent to read in an 8GB file just to remove a 100MB segment.

    BM> Is there another way to do this?

    BM> Is it possible to modify the inode structure of the underlying
    BM> filesystem to free blocks in the middle? (What to do with the half-full
    BM> blocks that are left?) Has anyone written a tool to do something like
    BM> this?

    BM> Is there a way to do this in a filesystem-independent manner?

    A COW fs is a far more useful and cool. A fs where a copy of a file
    does not duplicate all blocks. Blocks get copied-on-write only when
    copy of a file is written to. There could be even a fs compressor
    which looks for and merges blocks with exactly same contents from
    different files.

    Maybe ext2/3 folks will play with this idea after ext3?

    I'm planning to write a test program which will scan my ext2 fs and
    report how many duplicate blocks with the same contents it sees (i.e
    how many would I save with a COW fs)
    Best regards,

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