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

Robert Hancock
2007-03-24T22:12:55Z

Justin Piszcz wrote:
> Without NCQ, performance is MUCH better on almost every operation, with
> the exception of 2-3 items.
>
> /usr/sbin/bonnie++ -d /x/bonnie -s 7952 -m p34 -n 16:100000:16:64 >
> run.txt;
>
> # Average of 3 runs with NCQ on for Quad Raptor ADFD 150 RAID 5 Software
> RAID:
> p34-ncq-on,7952M,43916.3,96.6667,151943,28.6667,75794.3,18.6667,48991.3,99,181687,24,558.033,0.333333,16:100000:16/64,867.667,9,29972.7,98.3333,2801.67,16,890.667,9.33333,27743,94.3333,2115.33,15.6667
>
> # Average of 3 runs with NCQ off for Quad Raptor ADFD 150 RAID 5
> Software RAID:
> p34-ncq-off,7952M,42470,97.3333,200409,36.3333,90240.3,22.6667,48656,99,198853,27,546.467,0,16:100000:16/64,972.333,10,21833,72.3333,3697,21,995,10.6667,27901.7,95.6667,2681,20.6667
>
>
> http://home.comcast.net/~jpiszcz/ncq_vs_noncq/results.html
>
> In general, for networking, etc, the kernel chooses 'optimized'
> defaults, therefore, I was curious why is NCQ enabled by default?

Normally NCQ is faster, though it depends on the drive firmware. It's
also possible that software RAID is a case where there are negative
interactions.

--
Robert Hancock Saskatoon, SK, Canada
To email, remove "nospam" from hancockr@nospamshaw.ca
Home Page: http://www.roberthancock.com/