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 <pavel@xxxxxx> 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. - -When changes to the filesystem (e.g. a file is renamed) they are stored in -a transaction in the journal and can either be complete or incomplete at -the time of a crash. If a transaction is complete at the time of a crash -(or in the normal case where the system does not crash), then any blocks -in that transaction are guaranteed to represent a valid filesystem state, -and are copied into the filesystem. If a transaction is incomplete at -the time of the crash, then there is no guarantee of consistency for -the blocks in that transaction so they are discarded (which means any -filesystem changes they represent are also lost). +========== Check Documentation/filesystems/ext3.txt if you want to read more about ext3 and journaling. -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
