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SubjectRe: Disk performance degradation

On Thu, 31 Jul 2003, Andrew Morton wrote:

> mru@users.sourceforge.net (Mĺns Rullgĺrd) wrote:
> >
> > Mike Dresser <mdresser_l@windsormachine.com> writes:
> >
> > > Probably for reasons like that. For some reason, I can't set my ICH4
> > > based controller(ASUS P4B533) and Quantum Fireball AS40.0 to more than
> > > 255. Kernel is 2.4.21
> >
> > It appears that in 2.[56] kernels the unit for readahead is bytes,
> > rather than sectors, as used in 2.4 kernels.
>
> The ioctl which is used by
>
> blockdev --setra
>
> is still in 512-byte units.
>
> There are other backdoors such as IDE-private /proc files which can be used
> to set readahead. I'm not sure what units they use, and I don't know what
> mechanism hdparm is using to diddle readahead.

in 2.4.x:

/proc/ide/hdX/settings

breada_readahead - BLKRA{GET/SET}
file_readahead - BLKFRA{GET/SET}

both are in 1024 bytes units

in 2.6.x they are gone :-).

and hdparm is using BLKRA{GET/SET}

--
Bartlomiej

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