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    SubjectRe: DVD blockdevice buffers
    On Fri, May 18, 2001 at 09:25:31PM +0200, Jens Axboe wrote:
    > On Fri, May 18 2001, Eduard Hasenleithner wrote:
    > > I have a problem with the buffering mechanism of my blockdevice,
    > > namely a ide_scsi DVD-ROM drive. After inserting a DVD and reading
    > > data linearly from the DVD, an excessive amount of buffer memory gets
    > > allocated.
    > >
    > > This can easily be reproduced with
    > > cat /dev/sr0 > /dev/null
    > >
    > > Remember, nearly the same task is carried out when playing a DVD.
    > >
    > > As a result the system performance goes down. I'm still able to use
    > > my applications, but es every single piece of unused memory is swapped
    > > out, and swapping in costs a certain amount of time.
    > That's why streaming media applications like a dvd player should use raw
    > I/O -- to bypass system cache. See /dev/raw*

    Oh, thank you. That was very fast!

    I use xine. To be honest, the procedure of how to create a raw device
    is described in their FAQ. But it is not described, what the raw device
    does, only that it provides a speed improvement.

    Until today, I didn't know what rawio actually does. Strange that I didn't
    come across on some information about it.

    Was there a official announcement of the availability of this feature?
    Is some more detailled information about the rawio existing?

    Eduard Hasenleithner
    student of
    Salzburg University of Applied Sciences and Technologies
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