Message-ID: <43CE6363.2020402@cfl.rr.com>
Date: Wed, 18 Jan 2006 10:48:51 -0500
From: Phillip Susi <psusi@cfl.rr.com>
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To: Alan Cox <alan@lxorguk.ukuu.org.uk>
CC: "Jeff V. Merkey" <jmerkey@wolfmountaingroup.com>,
       Max Waterman <davidmaxwaterman@fastmail.co.uk>,
       linux-kernel@vger.kernel.org
Subject: Re: io performance...
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I was going to say, doesn't the kernel set the FUA bit on the write 
request to push important flushes through the disk's write-back cache?  
Like for filesystem journal flushes?


Alan Cox wrote:
> Not always. If you have a cache flush command and the OS knows about
> using it, or if you don't care if the data gets lost over a power
> failure (eg /tmp and swap) it makes sense to force it.
>
> The raid controller drivers that fake scsi don't always fake enough of
> scsi to report that they support cache flushes and the like. That
> doesn't mean the controller itself is neccessarily doing one thing or
> the other.
>
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