Date: Mon, 24 Jan 2011 13:53:51 +0100 From: Pawel Jakub Dawidek <pjd@FreeBSD.org> To: Bruce Cran <bruce@cran.org.uk> Cc: freebsd-fs@freebsd.org Subject: Re: Write cache, is write cache, is write cache? Message-ID: <20110124125351.GL1700@garage.freebsd.pl> In-Reply-To: <20110122172714.00002274@unknown> References: <1ABA88EDF84B6472579216FE@Octa64> <20110122111045.GA59117@icarus.home.lan> <D8077758CFED5EF1CB2AB613@Octa64> <20110122172714.00002274@unknown>
index | next in thread | previous in thread | raw e-mail
[-- Attachment #1 --] On Sat, Jan 22, 2011 at 05:27:14PM +0000, Bruce Cran wrote: > On Sat, 22 Jan 2011 15:51:21 +0000 > Karl Pielorz <kpielorz_lst@tdx.co.uk> wrote: > > > I'll have a look at those - I'm more interested in finding a tool > > that will write data both with, and without the "don't cache this" > > flag(s) set - to see if the performance is the same (you would hope > > that regardless of the BIOS setting that writing entirely data that's > > marked not to be cached, the performance would 'sink' back down to a > > sedate 12Mbytes/sec) - if it doesn't, something is lying somewhere :) > > sysutils/fio supports that: just add "fsync=x" to the > configuration file and it'll send a request to the OS to flush the data > to disk every x blocks. My guess (based on option name) is that it will perform fsync(2) every x blocks, which has nothing to do with disk write cache. Most file systems (unfortunately UFS is one of them) simply ignores existance of disk write caches. In Mac OS X you can find F_FULLFSYNC flag to fcntl(2) which is suppose to ask underlying disk to flush its cache. fsync(2) don't do that for UFS, but it does that for ZFS. -- Pawel Jakub Dawidek http://www.wheelsystems.com pjd@FreeBSD.org http://www.FreeBSD.org FreeBSD committer Am I Evil? Yes, I Am! [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.14 (FreeBSD) iEYEARECAAYFAk09dl4ACgkQForvXbEpPzSKrQCg+jOX9lX8ho3yf2F/L01+SbQi yTEAoLREzy5dzV3T2kMcxB1kroU59+Kg =vAsD -----END PGP SIGNATURE-----help
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20110124125351.GL1700>