Date: Wed, 27 Oct 2010 02:00:51 -0700 From: perryh@pluto.rain.com To: ivoras@freebsd.org Cc: freebsd-hackers@freebsd.org Subject: Re: fsync(2) manual and hdd write caching Message-ID: <4cc7ea44.ApOaxS8Xr4Sxu%2B0x%perryh@pluto.rain.com> In-Reply-To: <ia7nln$piv$1@dough.gmane.org> References: <20101026213618.GA3013@freebsd.org> <ia7nln$piv$1@dough.gmane.org>
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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. IMO, volatile RAM without battery backup cannot reasonably be considered a "permanent storage device", regardless of where it is physically located. Short of mounting synchronously, with the attendant performance hit, would it not make sense for fsync(2) to issue ATA_FLUSHCACHE or SCSI "SYNCHRONIZE CACHE" after it has finished writing data to the drive? Surely the low-level capability to issue those commands must already exist, else we would have no way to safely prepare for power off.help
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