From: Florian Weimer Subject: Re: [patch] ext2/3: document conditions when reliable operation is possible Date: Mon, 24 Aug 2009 11:19:01 +0000 Message-ID: <82k50tjw7u.fsf@mid.bfk.de> References: <20090312092114.GC6949@elf.ucw.cz> <200903121413.04434.rob@landley.net> <20090316122847.GI2405@elf.ucw.cz> <200903161426.24904.rob@landley.net> <20090323104525.GA17969@elf.ucw.cz> <87ljqn82zc.fsf@frosties.localdomain> <20090824093143.GD25591@elf.ucw.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Goswin von Brederlow , Rob Landley , kernel list , Andrew Morton , mtk.manpages@gmail.com, tytso@mit.edu, rdunlap@xenotime.net, linux-doc@vger.kernel.org, linux-ext4@vger.kernel.org To: Pavel Machek Return-path: In-Reply-To: <20090824093143.GD25591@elf.ucw.cz> (Pavel Machek's message of "Mon\, 24 Aug 2009 11\:31\:43 +0200") Sender: linux-doc-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org * Pavel Machek: > +Linux block-backed filesystems can only work correctly when several > +conditions are met in the block layer and below (disks, flash > +cards). Some of them are obvious ("data on media should not change > +randomly"), some are less so. You should make clear that the file lists per-file-system rules and that some file sytems can recover from some of the error conditions. > +* don't damage the old data on a failed write (ATOMIC-WRITES) > + > + (Thrash may get written into sectors during powerfail. And > + ext3 handles this surprisingly well at least in the > + catastrophic case of garbage getting written into the inode > + table, since the journal replay often will "repair" the > + garbage that was written into the filesystem metadata blocks. Isn't this by design? In other words, if the metadata doesn't survive non-atomic writes, wouldn't it be an ext3 bug? --=20 =46lorian Weimer BFK edv-consulting GmbH http://www.bfk.de/ Kriegsstra=DFe 100 tel: +49-721-96201-1 D-76133 Karlsruhe fax: +49-721-96201-99