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

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Message-ID: <460E5A51.7010601@emc.com>
Date:	Sat, 31 Mar 2007 08:55:45 -0400
From:	Ric Wheeler <ric@....com>
To:	Mark Rustad <mrustad@...il.com>
CC:	Jeff Garzik <jeff@...zik.org>,
	Justin Piszcz <jpiszcz@...idpixels.com>,
	linux-kernel@...r.kernel.org,
	IDE/ATA development list <linux-ide@...r.kernel.org>
Subject: Re: Why is NCQ enabled by default by libata? (2.6.20)



Mark Rustad wrote:
> On Mar 27, 2007, at 1:38 PM, Jeff Garzik wrote:
>
>> Mark Rustad wrote:
>>> reorder any queued operations. Of course if you really care about 
>>> your data, you don't really want to turn write cache on.
>>
>> That's a gross exaggeration.  FLUSH CACHE and FUA both ensure data 
>> integrity as well.
>>
>> Turning write cache off has always been a performance-killing action 
>> on ATA.
>
> Perhaps. Folks I work with would disagree with that, but I am not 
> enough of a storage expert to judge. My statement mirrors the 
> judgement of folks I work with that know more than I do.

You can easily demonstrate that disabling write cache on a S-ATA or ATA 
drive will drop your large file write performance by 50% - just try 
writing 10MB files to disk. 

ric


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