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SubjectRe: Disk performance degradation
mru@users.sourceforge.net (Måns Rullgård) 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.

Whatever it is, I suggest you ignore it and use /sbin/blockdev; it works
for all disk types.

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