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    SubjectRe: direct (unbufferd) disk access
    > 
    > On Mon, 28 Jun 1999 09:24:06 -0700 (PDT), Matthew Jacob
    > <mjacob@feral.com> said:
    >
    > >> On Sat, 26 Jun 1999 00:06:53 -0400, Douglas Gilbert
    > >> Given that we have clocked reasonably standard i386 hardware with fast
    > >> disks at 50 or 60 MB/sec through the filesystem, I doubt that the
    > >> indirect IO is the bottleneck in those cases.
    >
    > > Without cache pollution?
    >
    > Page cache pollution is a totally different issue. At 60MB/sec
    > we aren't even close to the performance levels where memory bandwidth
    > is an issue, so extra copies into the cache are irrelevant from a
    > bandwidth point of view. Of _course_ raw IO has less impact on
    > memory, but that's another point entirely.

    What I mean was: raw I/O is an application policy statement that says
    "leaving this data in the buffer cache is not what I want". You certainly
    do have some overhead in throwing stuff away if it's sitting in the buffer
    cache.


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