Date: Wed, 26 Jan 2005 15:03:46 -0800 (PST) From: Arne "Wörner" <arne_woerner@yahoo.com> To: David Schultz <das@FreeBSD.ORG> Cc: freebsd-fs@FreeBSD.ORG Subject: Re: ufs+softupdates / consistency Message-ID: <20050126230346.7958.qmail@web41213.mail.yahoo.com> In-Reply-To: <20050126212838.GA61425@VARK.MIT.EDU>
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--- 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? I have to admit, that I never tested ext2fs but ext3fs with unknown fs parameters (I just used mkfs_ext3fs (or so?)). > 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? I liked the idea of soft updates quite much, because it saves disc write accesses (as far as I understood it), so that I would like to continue to use ufs+softupd... > > 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? I could try to write some code, but I am quite unfamiliar with kernel program writing. Maybe this is not a fs@ subject but more a performance@ subject? -Arne __________________________________ Do you Yahoo!? Meet the all-new My Yahoo! - Try it today! http://my.yahoo.com
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