Date: Tue, 26 Oct 2010 20:07:05 +0100 From: Bruce Cran <bruce@cran.org.uk> To: "Marc G. Fournier" <scrappy@hub.org> Cc: freebsd-questions@freebsd.org Subject: Re: fsync: Linux vs FreeBSD Message-ID: <20101026200705.000006d1@unknown> In-Reply-To: <alpine.BSF.2.00.1010261530200.39682@hub.org> References: <alpine.BSF.2.00.1010261530200.39682@hub.org>
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On Tue, 26 Oct 2010 15:33:52 -0300 (ADT) "Marc G. Fournier" <scrappy@hub.org> wrote: > > Someone recently posted on one of the PostgreSQL Blogs concerning > fsync on Linux/Windows/Mac OS X, but failed to make any comments on > any of the BSDs ... the post has to do with how fsync works on the > various OSs, and am curious as to whether or not this is something > that also afflicts us: > > http://rhaas.blogspot.com/2010/10/wal-reliability.html > > >From reading our man page, I see no warnings similar to what the > >other OSs > have, specifically: > > Mac OS X: For applications that require tighter guarantees about the > integrity of their data, Mac OS X provides the F_FULLFSYNC > fcntl > > Linux: If the underlying hard disk has write caching enabled, then the > data may not really be on permanent storage when fsync() / > fdatasync() return. > > So, do we hide the fact, or are, in fact, not afflicted by this? Yes, it is a problem: http://leaf.dragonflybsd.org/mailarchive/kernel/2010-01/msg00007.html There also a paragraph on write cache and filesystem integrity in da(4): http://www.freebsd.org/cgi/man.cgi?query=da&apropos=0&sektion=0&manpath=FreeBSD+8.1-RELEASE&format=html -- Bruce Cran
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