Brad Walker writes:

>> From: bad@flatlin.ka.sub.org (Christoph Badura)
>> Except the buffer cache and the disksort routine are supposed to do
>> that already.

>But, they don't optimize for head actuator position.

Huh?  That's what the disksort routine is supposed to take care of.

Except, of course, with devices that remap bad sectors to far away
tracks behind the initiators back.

>> It could well be that the target gets it wrong and the performance
>> gets worse.  There is a CSRG paper about such an experience with a
>> non-SCSI controller that did it's own ordering.

>Quote your source.. 

Kridle, R., and McKusick, M., "Performance Effects of Disk Subsystem
Choices for VAX Systems Running 4.2BSD UNIX", CSRG, Dept of EECS, UCB
technical report #8, 1983

>And it is worth mentioning that this is paper is
>most likely quite a few years old. Before current technology.

I don't think someone has invented a way for disk controller firmware
to divine the optimal execution order of requests in the last 13
years.

The performance problems were with the disk controller re-ordering the
requests.  They went away when they disabled that "feature."

-- 
Christoph Badura	bad@flatlin.ka.sub.org

You don't need to quote my .signature.  Everyone has seen it by now.
Besides, it doesn't add anything to the current thread.