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From: Scott Long <scottl@samsco.org>
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Date: Fri, 1 Jan 2010 17:03:03 -0700
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To: Poul-Henning Kamp <phk@phk.freebsd.dk>
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Cc: Alexander Motin <mav@freebsd.org>, Miroslav Lachman <000.fbsd@quip.cz>,
	Thomas Backman <serenity@exscape.org>,
	freebsd-current@freebsd.org, freebsd-arch@freebsd.org,
	Pieter de Goeje <pieter@degoeje.nl>
Subject: Re: File system blocks alignment 
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On Jan 1, 2010, at 3:47 PM, Poul-Henning Kamp wrote:
> In message <201001012153.44349.pieter@degoeje.nl>, Pieter de Goeje  
> writes:
>
>> That yielded some pretty spectacular results. [...]
>>
>> Performance for restore was abysmal in the unaligned case, easily  
>> being 10
>> times slower than aligned restore. Newfs was about 5 times as slow.
>
> That is what I expected, only I didn't expect a factor 14 in  
> performance.
>

It's all about read latency in the read-modify update operation.   
While buses and caches and gotten steadily faster over the past 20  
years, disk platters and hysteresis fields have not.  This is also why  
buying faster platters is always an important consideration for  
overall performance; a desktop or laptop with 5400RPM drives will feel  
significantly slower than one with 7200RPM drives, and 15K RPM drives  
still rule the roost.

Thanks a lot for doing the testing.  Would it be possible to publish  
these results somewhere that can be linked to in the future?

Scott