Date: Tue, 06 Feb 2001 21:19:23 +0100 From: Andre Oppermann <oppermann@monzoon.net> To: Matt Dillon <dillon@earth.backplane.com> Cc: Mike Silbersack <silby@silby.com>, Rik van Riel <riel@conectiva.com.br>, Poul-Henning Kamp <phk@critter.freebsd.dk>, 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: <3A805C4B.A200EA28@monzoon.net> References: <Pine.BSF.4.31.0102061149180.14899-100000@achilles.silby.com> <200102061759.f16Hxv662437@earth.backplane.com> <3A805137.230E0A0D@monzoon.net> <200102061956.f16JuCb65538@earth.backplane.com>
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Matt Dillon wrote: > > : > :This information is in fact correct. Have a look at the FreeBSD link(2) > :man page: > : > :LINK(2) FreeBSD System Calls Manual > :LINK(2) > > Andre, I think there *might* be a dozen people in the world that > understand UFS/FFS better then I do, but none of them have posted to > this thread. > > Believe me when I say that there is no metadata ordering guarentee > in the case of a crash. Yes a standard UFS/FFS will do synchronous > metadata updates for certain operations. No, this does not guarentee > metadata ordering. OK, then I believe you. But please answer me one question: Is the link() call atomically in FFS/UFS w or w/o softupdates? Meaning when the call returns the meta- data is written to stable storage like with fsync()? Only this answer is needed for qmail operation. -- Andre > There has been talk of providing system calls to allow user programs > to request ordering semantics for certain operations, but nobody has > actually implemented anything. Most of the discussion has been centered > on having calls to guarentee file write ordering between a set of > open descriptors for databases. > > As I said, a journaled filesystem can theoretically make metadata > ordering guarentees, but actually doing so creates massive performance > and scaleability issues that aren't apparent until you really start > pounding the filesystem. It *CAN* be done efficiently, but only if > you have a significant amount of non-volatile memory store to hold > the journal. ReiserFS might do it right now, as a side effect, but if > it does it faces serious scaleability issues. > > Softupdates can also theoretically order [meta]data, using dependancies. > It is a very difficult problem to solve and it doesn't do it now. All > softupdates does is guarentee filesystem consistency in the case of a > crash and certain guarentees for what will be crash-recoverable when you > do an fsync(). > > -Matt To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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