linux-kernel - Re: Proposal for "proper" durable fsync() and fdatasync()

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Message-ID: <47C40269.7060309@emc.com>
Date:	Tue, 26 Feb 2008 07:13:29 -0500
From:	Ric Wheeler <ric@....com>
To:	Jeff Garzik <jeff@...zik.org>
CC:	Jamie Lokier <jamie@...reable.org>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, Chris Wedgwood <cw@...f.org>
Subject: Re: Proposal for "proper" durable fsync() and fdatasync()

Jeff Garzik wrote:
> Jamie Lokier wrote:
>> By durable, I mean that fsync() should actually commit writes to
>> physical stable storage,
> 
> Yes, it should.
> 
> 
>> I was surprised that fsync() doesn't do this already.  There was a lot
>> of effort put into block I/O write barriers during 2.5, so that
>> journalling filesystems can force correct write ordering, using disk
>> flush cache commands.
>>
>> After all that effort, I was very surprised to notice that Linux 2.6.x
>> doesn't use that capability to ensure fsync() flushes the disk cache
>> onto stable storage.
> 
> It's surprising you are surprised, given that this [lame] fsync behavior 
> has remaining consistently lame throughout Linux's history.

Maybe I am confused, but isn't this is what fsync() does today whenever 
barriers are enabled (the fsync() invalidates the drive's write cache).

ric
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