Re: the '--setra 65536' mistery, analysis and WTF?

[Nat Makarevitch <nat@makarevitch.org>]

Peter Grandi <pg_lxra <at> lxra.for.sabi.co.UK> writes:

> this seems to indicate that not only the Linux block IO subsystems issues
> IO operations in multiples of the read-ahead size, but does so at a fixed
> number of times per second that is a multiple of 10.

Is it the case with a classic controller (not a 3ware?)

http://forums.storagereview.net/index.php?showtopic=25923 may be of
interest.

> Which lead me to think about elevators, which was also mentioned
> in some recent (and otherwise less interesting :->)

Sorry, I don't understand this.

> It still seems the case to me that the block IO subsystem
> structures IO in lots of read-ahead sectors

Isn't it specific to the 3ware driver and/or hardware, even in
SINGLE (JBOD) mode?

> Finally, I am getting a bit skeptical about elevators in general;

> several tests show no-elevator as not being significantly worse
> and sometimes better than any elevator

Isn't it specific to intelligent controllers?