Re: Why is NCQ enabled by default by libata? (2.6.20)

[Justin Piszcz]

On Sat, 24 Mar 2007, Alan Cox wrote:

> On Sat, 24 Mar 2007 12:38:02 -0400 (EDT)
> Justin Piszcz <jpiszcz@xxxxxxxxxxxxxxx> wrote:
>
> > Without NCQ, performance is MUCH better on almost every operation, with
> > the exception of 2-3 items.
>
> It depends on the drive. Generally NCQ is better but some drive firmware
> isn't too bright and there are probably still cases where we get bad
> interactions in the kernel code that want tuning too

Checking the benchmarks on various hardware websites, anandtech, 
hothardware and others, they generally all come to the same conclusion if 
there is only 1 thread using I/O (single user system) then NCQ off is the 
best.  I see 30-50MB/s faster speeds with NCQ turned off on two different 
SW RAID5s.

Justin.
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