Date: Tue, 06 Feb 2001 20:19:57 +0100 From: Andre Oppermann <oppermann@monzoon.net> To: Poul-Henning Kamp <phk@critter.freebsd.dk> Cc: Matt Dillon <dillon@earth.backplane.com>, Charles Randall <crandall@matchlogic.com>, Dan Phoenix <dphoenix@bravenet.com>, Alfred Perlstein <bright@wintelcom.net>, Jos Backus <josb@cncdsl.com>, freebsd-hackers@FreeBSD.ORG Subject: Re: soft updates and qmail (RE: qmail IO problems) Message-ID: <3A804E5D.97BA622C@monzoon.net> References: <36088.981481432@critter>
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Poul-Henning Kamp wrote: > > In message <200102061739.f16HdOB61963@earth.backplane.com>, Matt Dillon writes: > > > >: > >:In message <5FE9B713CCCDD311A03400508B8B3013054E3F5D@bdr-xcln.is.matchlogic.com>, Charles Randall writes: > >:>The qmail FAQ specifically recommends against soft updates for the mail > >:>queue. > >:> > >:>http://cr.yp.to/qmail/faq/reliability.html#filesystems > >:> > >:>Is this incorrect? > >:> > >: > >:It seems to indicate that qmail doesn't use fsync(2) as much as it should > >:do. If that is true, then yes, softupdates would mean that a lot of things > >:which qmail (mistakenly) think has been written are in fact not on the > >:disk. > >: > >:-- > >:Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 > >:phk@FreeBSD.ORG | TCP/IP since RFC 956 > >:FreeBSD committer | BSD since 4.3-tahoe > >:Never attribute to malice what can adequately be explained by incompetence. > > > > QMail's FAQ is totally incorrect. No major filesystem -- be it > > FFS, EX2FS, Reiser, FFS+Softupdates, guarentees that when you > > write() and close() a file that the file will then survive a disk > > crash. All these filesystems guarentee is that if a crash occurs, > > when the system reboots the filesystems will be recovered into a > > consistent state. Softupdates is considerably better at guarenteeing > > this consistency (as is something like Reiser), but if you crash a > > softupdates disk may wind up unwinding 'more' of the last few moments > > worth of operations then a normal filesystem would. And, I might add, > > Reiser is the same way. > > > > The only way to guarentee that file data is written to disk, with any > > filesystem no matter how it is mounted (even sync mounted filesystems), > > is by calling fsync(). > > > > So I would stick with softupdates. > > ... provided that qmail calls fsync(2). $ cd qmail-ldap/ $ grep fsync * | wc -l 21 $ Twenty-one times in qmail(-ldap) seems to be enough... -- Andre To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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