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Date: Fri, 5 Jul 2013 08:24:31 -0700
From: Christoph Hellwig <hch@infradead.org>
To: Zoltan Arnold NAGY <zoltan.arnold.nagy@gmail.com>
Subject: Re: O_DIRECT|O_SYNC semantics?
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On Wed, Jul 03, 2013 at 09:05:40PM +0200, Zoltan Arnold NAGY wrote:
> Hi,
> 
> Could someone have a look here:
> http://serverfault.com/questions/520141/please-explain-my-fio-results-is-o-synco-direct-misbehaving-on-linux
> 
> Basically, I'm seeing wastly different results on Linux and on FreeBSD 9.1.
> Either FreeBSD's not honoring O_SYNC properly, or Linux does something
> wicked.
> 
> I've been at it for a few days, without any real progress.

For consumer disks using O_SYNC on Linux does make a huge difference,
because it flushes the disk write cache after completion to make sure
the O_SYNC gurantees that data has hit physical storage are met.

It seems like FreeBSD might be missing that call.