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

[Robert Hancock <hancockr@shaw.ca>]

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
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