Date: Thu, 29 Jun 2006 20:47:03 +1000 (EST) From: Bruce Evans <bde@zeta.org.au> To: Leo Huang <leo.huang.gd@gmail.com> Cc: freebsd-fs@freebsd.org, Ivan Voras <ivoras@fer.hr> Subject: Re: Is the fsync() fake on FreeBSD6.1? Message-ID: <20060629201157.N77878@delplex.bde.org> In-Reply-To: <a0cd7c070606281920r34fcc9dfr241ae6ac662024e4@mail.gmail.com> References: <a0cd7c070606270032h3a42de6ahf21cd11abedb6400@mail.gmail.com> <44A1B958.4030204@fer.hr> <20060628230439.M75051@delplex.bde.org> <a0cd7c070606281920r34fcc9dfr241ae6ac662024e4@mail.gmail.com>
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On Thu, 29 Jun 2006, Leo Huang wrote: >> >> OS Clients Result(queries per second) TPS(got from >> >> iostat) >> >> FreeBSD6.1 50 516.1 about 2000 >> >> Seems normal for drives that do write caching. > > I disable the driver write caching as Bjorn Gronvall suggest, the > result show that the TPS come down to about 200. So I think you and > Bjorn Gronvall are right. It is the disk write caching make the TPS so > high. > >> >> Debian3.1 50 49.8 about 200 >> >> Seems to slow for disks that do write caching. Maybe Debian does something >> to force the drive to complete it's i/o, or just does a full sync() like >> someone mentioned Linux doing. > > I use sginfo the find that the disk write caching is also enabled > default. After the disk write caching is disabled, the TPS also come > down from 200 to 110. This is really pullze me. Can you give me more > infomation about it? How did you disable "driver" write caching? I think both Bjorn and I meant the _drive_ write caching, and that is what you refer to as "disk" write caching. Only turn off the caching in the lowest layer (disk == drive). I wonder when all drives will have enough fast enough nonvolatile RAM for write caching to just work. Bruce
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