Date: Tue, 06 Feb 2001 18:43:52 +0100 From: Poul-Henning Kamp <phk@critter.freebsd.dk> To: Matt Dillon <dillon@earth.backplane.com> Cc: 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: <36088.981481432@critter> In-Reply-To: Your message of "Tue, 06 Feb 2001 09:39:24 PST." <200102061739.f16HdOB61963@earth.backplane.com>
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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). -- 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. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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