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

Justin Piszcz
2007-03-27T09:55:46Z

On Sat, 24 Mar 2007, Alan Cox wrote:

> On Sat, 24 Mar 2007 12:38:02 -0400 (EDT)
> Justin Piszcz <jpiszcz@lucidpixels.com> 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.