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Sender: Alexander Motin <mavbsd@gmail.com>
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Date: Thu, 03 Dec 2009 11:22:35 +0200
From: Alexander Motin <mav@FreeBSD.org>
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Subject: Re: NCQ vs UFS/ZFS benchmark [Was: Re: FreeBSD 8.0 Performance (at
 Phoronix)]
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Ivan Voras wrote:
> Alexander Motin wrote:
>> Data doesn't fit into cache. Multiple parallel requests give some effect
>> even with legacy driver, but with NCQ enabled it gives much more, almost
>> doubling performance!
> 
> You've seen queueing in gstat for ZFS+NCQ?

Yes. All the time 32+ requests per drive, when multiple processes
running. That's why enabling NCQ gave such effect.

Some speedup in legacy driver case on multiple processes could probably
be explained by elevator sorter work in disk driver. It was very audible
that drive work in cycles.

-- 
Alexander Motin