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    SubjectRe: [RFC] ext3: per-process soft-syncing data=ordered mode
    On Jan 24, 2008  23:36 +0300, Al Boldi wrote:
    > data=ordered mode has proven reliable over the years, and it does this by
    > ordering filedata flushes before metadata flushes. But this sometimes
    > causes contention in the order of a 10x slowdown for certain apps, either
    > due to the misuse of fsync or due to inherent behaviour like db's, as well
    > as inherent starvation issues exposed by the data=ordered mode.
    > data=writeback mode alleviates data=order mode slowdowns, but only works
    > per-mount and is too dangerous to run as a default mode.
    > This RFC proposes to introduce a tunable which allows to disable fsync and
    > changes ordered into writeback writeout on a per-process basis like this:
    > echo 1 > /proc/`pidof process`/softsync

    If fsync performance is an issue for you, run the filesystem in data=journal
    mode, put the journal on a separate disk and make it big enough that you
    don't block on it to flush the data to the filesystem (but not so big that
    it is consuming all of your RAM).

    That keeps your data guarantees without hurting performance.

    Cheers, Andreas
    Andreas Dilger
    Sr. Staff Engineer, Lustre Group
    Sun Microsystems of Canada, Inc.

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      Last update: 2008-01-25 21:27    [W:2.997 / U:0.004 seconds]
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