From owner-freebsd-hackers Tue Feb 6 9:42:25 2001 Delivered-To: freebsd-hackers@freebsd.org Received: from earth.backplane.com (earth-nat-cw.backplane.com [208.161.114.67]) by hub.freebsd.org (Postfix) with ESMTP id D4A5B37B503 for ; Tue, 6 Feb 2001 09:42:06 -0800 (PST) Received: (from dillon@localhost) by earth.backplane.com (8.11.1/8.9.3) id f16HdOB61963; Tue, 6 Feb 2001 09:39:24 -0800 (PST) (envelope-from dillon) Date: Tue, 6 Feb 2001 09:39:24 -0800 (PST) From: Matt Dillon Message-Id: <200102061739.f16HdOB61963@earth.backplane.com> To: Poul-Henning Kamp Cc: Charles Randall , Dan Phoenix , Alfred Perlstein , Jos Backus , freebsd-hackers@FreeBSD.ORG Subject: Re: soft updates and qmail (RE: qmail IO problems) References: <35545.981478627@critter> Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG : :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. -Matt To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message