Date: Wed, 26 Jan 2005 19:40:13 -0500 From: David Schultz <das@FreeBSD.ORG> To: Arne WXrner <arne_woerner@yahoo.com> Cc: freebsd-fs@FreeBSD.ORG Subject: Re: ufs+softupdates / consistency Message-ID: <20050127004013.GA62561@VARK.MIT.EDU> In-Reply-To: <20050126230346.7958.qmail@web41213.mail.yahoo.com> References: <20050126212838.GA61425@VARK.MIT.EDU> <20050126230346.7958.qmail@web41213.mail.yahoo.com>
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On Wed, Jan 26, 2005, Arne WXrner wrote: > --- David Schultz <das@FreeBSD.ORG> wrote: > > ext2fs mounted async does not provide consistency; in fact the > > state of the disk can be almost arbitrarily inconsistent at any > > given time. Soft updates is supposed to provide performance > > comparable to async writes without the inconsistency problem. > > I'm not sure what it is about your setup that causes such a > > disparity. (Many factors such as the FS block size and ATA write > > caching can make a big difference.) > > > Somebody in list freebsd-performance@ opened a thread "FreeBSD 5.3 > I/O Performance / Linux 2.6.10 | Continued Discussion", where he > and one other state, that FreeBSD R4.11 beforms much better (twice > faster) than FreeBSD R5.3. > > Could the disparity I saw be caused by the SMPng project in R5.3? It's certainly possible. > > By the way, ext3fs uses journalling, which provides metadata > > consistency in a very different way from soft updates. You > > might also want to experiment with that to see if it works > better > > for your workload. > > > Hmm... I do not understand this hint. > > Does FreeBSD offer a journaling file system? No, although an interest in UFS+journalling has been expressed by someone who could make it happen. Also, Jean-Sebastien Pedron has been working on a port of ReiserFS to FreeBSD. > > > Are we already trying to issue write order requests for the > > > disc blocks (whose write order is arbitrary) sorted by sector > > > number (in order to move the disc heads as less as possible)? > > > The disc write cache could do that, but I disabled it in order > > > to decrease the probability of inconsistency. > > > > Hopefully you disabled it on both FreeBSD and Linux, so you're > > comparing apples to apples... > > > During the tests I enabled write cache in both settings, because I > did not know how to turn it off in KNOPPIX... > > Isn't it possible to simulate the hard disc write cache in kernel? The write caching will make a big difference. Sorry, but I don't know how to turn it off under Linux. Perhaps you could turn it on under FreeBSD for the purpose of your performance analysis.home | help
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