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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.ysu.edu!usenet.ins.cwru.edu!pravda.aa.msen.com!nntp.coast.net!zombie.ncsc.mil!news.mathworks.com!newsfeed.internetmci.com!in1.uu.net!news.artisoft.com!not-for-mail From: mday@elbereth.org (Matt Day) Newsgroups: comp.unix.bsd.freebsd.misc,comp.os.linux.development.system Subject: Re: The better (more suitable)Unix?? FreeBSD or Linux Date: 7 Mar 1996 12:41:59 -0700 Organization: none Lines: 35 Message-ID: <4hne67$qq@coyote.Artisoft.COM> References: <Dnu8FD.CK2@pe1chl.ampr.org> <4hl00v$7it@coyote.Artisoft.COM> <Dnw3qn.G29@pe1chl.ampr.org> NNTP-Posting-Host: coyote.artisoft.com Xref: euryale.cc.adfa.oz.au comp.unix.bsd.freebsd.misc:14943 comp.os.linux.development.system:18748 In article <Dnw3qn.G29@pe1chl.ampr.org> pe1chl@wab-tis.rabobank.nl writes: >The examples in your summary only show the well-known cases of files >or blocks being lost when the system crashes. The problem can only >occur with files that were being modified at the time of the crash. >As we know by now, the content of such files is not reliably known >anyway (because of delayed data writes). I agree, after a system crash you may not know exactly what data is in the files you were writing to at the time of the crash. But, if your file system sequences its metadata updates, then you will at least know that either the data is old (the delayed data write or the associated sequenced metadata changes never made it to disk) or new (the delayed data write made it to disk, along with the associated sequenced metadata changes). If your file system does not sequence its metadata updates, then a third possibility presents itself: the data is garbage. This third possibility is worth eliminating, because it is good to know that your files will never contain garbage, and it also closes a security hole since the garbage might be sensitive data from someone else's deleted file. If anyone does not believe what I have said here is true, then please go read the technical reports on the matter. This one is a good start: http://www.pdos.lcs.mit.edu/~ganger/papers/CSE-TR-254-95/ >None of your examples shows how "you could loose *every* file on an >active filesystem", and I still think this is FUD. I agree, I can't think of a scenario where unsequenced metadata updates could cause the loss of the entire file system. (Assuming your fsck doesn't grossly screw up the cases that it can't fix.) The summary was directed at the general confusion on the matter. (Sorry if I didn't make that clear.) Matt Day <mday@elbereth.org>