From: Pavel Machek Subject: [patch] document that ext2 can't handle barriers Date: Wed, 26 Aug 2009 00:27:23 +0200 Message-ID: <20090825222723.GC4300__10521.465217653$1251239283$gmane$org@elf.ucw.cz> References: <20090824195159.GD29763@elf.ucw.cz> <4A92F6FC.4060907@redhat.com> <20090824205209.GE29763@elf.ucw.cz> <4A930160.8060508@redhat.com> <20090824212518.GF29763@elf.ucw.cz> <20090824223915.GI17684@mit.edu> <20090824230036.GK29763@elf.ucw.cz> <20090825000842.GM17684@mit.edu> <20090825094244.GC15563@elf.ucw.cz> <20090825161110.GP17684@mit.edu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii To: Theodore Tso , Ric Wheeler , Florian Weimer , Goswin von Brederlow , Rob Landley , kernel list Return-path: Received: from atrey.karlin.mff.cuni.cz ([195.113.26.193]:40569 "EHLO atrey.karlin.mff.cuni.cz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756267AbZHYW1c (ORCPT ); Tue, 25 Aug 2009 18:27:32 -0400 Content-Disposition: inline In-Reply-To: <20090825161110.GP17684@mit.edu> Sender: linux-ext4-owner@vger.kernel.org List-ID: Document things ext2 expects from storage filesystems, and the fact that it can not handle barriers. Also remove jounaling description, as that's really ext3 material. Signed-off-by: Pavel Machek diff --git a/Documentation/filesystems/ext2.txt b/Documentation/filesystems/ext2.txt index 67639f9..e300ca8 100644 --- a/Documentation/filesystems/ext2.txt +++ b/Documentation/filesystems/ext2.txt @@ -338,27 +339,17 @@ enough 4-character names to make up unique directory entries, so they have to be 8 character filenames, even then we are fairly close to running out of unique filenames. +Requirements +============ + +Ext2 expects disk/storage subsystem not to return write errors. + +It also needs write caching to be disabled for reliable fsync +operation; ext2 does not know how to issue barriers as of +2.6.31. hdparm -W0 disables it on SATA disks. + Journaling ----------- - -A journaling extension to the ext2 code has been developed by Stephen -Tweedie. It avoids the risks of metadata corruption and the need to -wait for e2fsck to complete after a crash, without requiring a change -to the on-disk ext2 layout. In a nutshell, the journal is a regular -file which stores whole metadata (and optionally data) blocks that have -been modified, prior to writing them into the filesystem. This means -it is possible to add a journal to an existing ext2 filesystem without -the need for data conversion.