From mboxrd@z Thu Jan 1 00:00:00 1970 From: pamvdam@ramoth.xs4all.nl Date: Mon, 4 Oct 1999 13:03:12 +0200 Subject: Re: [linux-lvm] LVM, raw-io, devfs Message-ID: <19991004130312.A19918@ladystrange.bluehorizon.nl> References: <006201bf0bb7$6eae4a60$030116ac@fd1> <14324.58266.920834.895229@dukat.scot.redhat.com> <002e01bf0cf8$b4667720$030116ac@fd1> <19991003075644.A5224@ladystrange.bluehorizon.nl> <14328.33999.21844.718869@dukat.scot.redhat.com> Mime-Version: 1.0 In-Reply-To: <14328.33999.21844.718869@dukat.scot.redhat.com>; from Stephen C. Tweedie on Mon, Oct 04, 1999 at 11:43:27AM +0100 Sender: owner-linux-lvm Errors-To: owner-linux-lvm List-Id: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: "Stephen C. Tweedie" Cc: pamvdam@ramoth.xs4all.nl, Fernando Dammous , Linux LVM msede On Mon, Oct 04, 1999 at 11:43:27AM +0100, Stephen C. Tweedie wrote: > Hi, > > On Sun, 3 Oct 1999 07:56:44 +0200, pamvdam@ramoth.xs4all.nl said: > > > Oracle has always been using filesystems for it's datastorage. Only for > > the parrallel server configuration they demand RAW IO. Like Sybase 11.9.x > > under Linux it probably uses some O_SYNC flag to write to log, so the > > write call only returns when the data has been really written to the > > physical device. I don't think you'll see a performance enhancement when > > using Oracle and RAW/IO. There's even a chance, due to the fact you mis > > the buffer cache optimisations, that you'll see a performance > > degradation. > > It depends. Raw IO uses less CPU --- much less in some cases. It also > avoids polluting memory with extra copies of data in the buffer cache. > As a result, just measuring the pure disk bandwidth of raw IO versus > buffered IO does not tell you the whole story about performance: you > really need to measure the application's performance itself, including > the effect of CPU and memory pressure. You're right. I did oversee the buffercache pollution issue. Thanks for pointing it out. Best regards, Pascal > > --Stephen