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Newsgroups: comp.unix.bsd.freebsd.misc,comp.os.linux.development.system Path: euryale.cc.adfa.oz.au!newshost.anu.edu.au!harbinger.cc.monash.edu.au!news.mel.connect.com.au!munnari.OZ.AU!news.ecn.uoknor.edu!news.cis.okstate.edu!news.ksu.ksu.edu!news.physics.uiowa.edu!newsrelay.iastate.edu!vixen.cso.uiuc.edu!newsfeed.internetmci.com!EU.net!sun4nl!rnzll3!sys3.pe1chl!rob From: rob@pe1chl.ampr.org (Rob Janssen) Subject: Re: async or sync metadata [was: FreeBSD v. Linux] Reply-To: pe1chl@wab-tis.rabobank.nl Organization: PE1CHL Message-ID: <DMnow5.43G@pe1chl.ampr.org> References: <4er9hp$5ng@orb.direct.ca> <DMI5Mt.768@pe1chl.ampr.org> <4fi6gq$3tr@dyson.iquest.net> <4fjodc$o8j@venger.snds.com> <jlemonDMMDq5.1yF@netcom.com> Date: Mon, 12 Feb 1996 09:26:28 GMT Lines: 42 Xref: euryale.cc.adfa.oz.au comp.unix.bsd.freebsd.misc:14092 comp.os.linux.development.system:17706 In <jlemonDMMDq5.1yF@netcom.com> jlemon@netcom.com (Jonathan Lemon) writes: >In article <4fjodc$o8j@venger.snds.com>, >Michael Griffith <grif@hill.ucr.edu> wrote: >>|In article <DMI5Mt.768@pe1chl.ampr.org>, >>|Rob Janssen <pe1chl@wab-tis.rabobank.nl> wrote: >>|>It seems to be very hard to get this misconception out of the BSD people's >>|>heads... >>|>Sync metadata writes may seem to improve things, but actually it just >>|>causes your fsck's to return no errors while the files are still >>|>corrupted. Not necessarily better. >> >>Very hard indeed. Here it is one more time: >> >> sync metadata with async data is not just slower, >> it is LESS SAFE. This behavour should not be the default >> on any reasonable system. If you want real safety, >> then both data and meta need to be synchronous (i.e. no >> buffer cache for writes). This real safety comes with >> an huge performance hit (as in MSDOS). >Um, Michael, Rob? Sync metadata just insures that the _filesystem_ is always >in a consistent state, not the data itself. It is safer in the sense that >you don't lose the entire filesystem, not that you don't lose data. Essentially, with sync metadata you will have to remove all recently modified files off your disk after a crash, because you cannot be sure of the validity of their contents. With ext2fs you won't lose the entire filesystem just because some metadata is not in a consistent state. fsck will fix that, and you will know about it (instead of having some false trust that everythink is OK). I don't know how FFS behaves in this regard, it may be true that you lose your entire filesystem if some inode or free space map has not been properly updated, but that would not be a clever design IMHO. Rob -- +------------------------------------+--------------------------------------+ | Rob Janssen rob@knoware.nl | BBS: +31-302870036 (2300-0730 local) | | AMPRnet: rob@pe1chl.ampr.org | AX.25 BBS: PE1CHL@PI8WNO.#UTR.NLD.EU | +------------------------------------+--------------------------------------+