Date: Wed, 27 Oct 2010 00:28:49 +0100 From: Bruce Cran <bruce@cran.org.uk> To: Ivan Voras <ivoras@freebsd.org> Cc: freebsd-hackers@freebsd.org Subject: Re: fsync(2) manual and hdd write caching Message-ID: <20101027002849.00002772@unknown> In-Reply-To: <ia7nln$piv$1@dough.gmane.org> References: <20101026213618.GA3013@freebsd.org> <ia7nln$piv$1@dough.gmane.org>
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On Wed, 27 Oct 2010 01:19:18 +0200 Ivan Voras <ivoras@freebsd.org> wrote: > fsync(2) actually does behave as advertised, "auses all modified data > and attributes of fd to be moved to a permanent storage device". It > is the problem of the "permanent storage device" if it caches this > data further. http://www.opengroup.org/onlinepubs/009695399/functions/fsync.html at first suggests it should flush write caches, but does allow for implementations that don't: "The fsync() function is intended to force a physical write of data from the buffer cache, and to assure that after a system crash or other failure that all data up to the time of the fsync() call is recorded on the disk." ... "In the middle ground between these extremes, fsync() might or might not actually cause data to be written where it is safe from a power failure." -- Bruce Cran
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