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    SubjectRe: [OFFTOPIC] Re: disk head scheduling
    In article <>,
    Stephen C. Tweedie <> wrote:
    >On Sun, 21 Mar 1999 11:49:31 -0800, (Jim Gettys) said:
    >indexed by block numbers). If the filesystem can also deallocate such
    >space, then we have an abstraction behind which filesystem shrinking

    As a side-effect this would help make devices built on FLASH memory a little
    easier to deal with. FLASH has the interesting principle of being able to
    be written from 1 to 0 at any time, But writing a 0 to a 1 requires erasing
    a (relatively) large block. The end result is that rewriting a single block
    can involve copying about 100k of data from one area to another.

    If the filesystem can tell the device layer that a block is no longer being
    used then the device layer can stop moving it around when erasing. This not
    only speeds that operation but opens up more empty space to copy new data
    to. [The device layer doesn't erase to rewrite blocks, it marks it as unused
    and writes it to somewhere that is currently not being used. It only erases
    when it runs out of empty blocks and needs to recover some.]

    Stuart Lynne <> 604-461-7532 <>
    PGP Fingerprint: 28 E2 A0 15 99 62 9A 00 88 EC A3 EE 2D 1C 15 68

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