Point one, the comments that Eric made do not give the complete picture.
All the tests that Eric's referring to were done through ZFS filesystem.
When sequential I/O is done to the disk directly there is no performance
degradation at all.  Second point,  it does not take any additional
time in ldi_strategy(), bdev_strategy(), mv_rw_dma_start().  In some
instance it actually takes less time.   The only thing that sometimes
takes additional time is waiting for the disk I/O.

Regards,
Lida

eric kustarz wrote:

I've been looking into the performance impact of NCQ. Here's what i found out:
http://blogs.sun.com/erickustarz/entry/ncq_performance_analysis

Curiously, there's not too much performance data on NCQ available via a google search ...

enjoy,
eric

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