On Thu, 2004-12-02 at 18:31 -0600, Alex White wrote: > Ext3 has journaling. What this means for you is that the system journals > disc activity so as if somethin' horrible happens; let's say a power > failure in the middle of a disc write or something like that, then the > journal will ease recovery. The journal allows the system to replay the > last actions taken up to the point of failure and then continue on as if > nothing ever happened. Ext3 is the default for Fedora. Actually, there's more to it than that. There are three different journaling modes supported by ext3 as quoted from the Linux source tree in Documentation/filesystems/ext3.txt and please note the default is metadata only journaling. Data Mode --------- There's 3 different data modes: * writeback mode In data=writeback mode, ext3 does not journal data at all. This mode provides a similar level of journaling as XFS, JFS, and ReiserFS in its default mode - metadata journaling. A crash+recovery can cause incorrect data to appear in files which were written shortly before the crash. This mode will typically provide the best ext3 performance. * ordered mode In data=ordered mode, ext3 only officially journals metadata, but it logically groups metadata and data blocks into a single unit called a transaction. When it's time to write the new metadata out to disk, the associated data blocks are written first. In general, this mode perform slightly slower than writeback but significantly faster than journal mode. * journal mode data=journal mode provides full data and metadata journaling. All new data is written to the journal first, and then to its final location. In the event of a crash, the journal can be replayed, bringing both data and metadata into a consistent state. This mode is the slowest except when data needs to be read from and written to disk at the same time where it outperform all others mode. -- C. Linus Hicks <lhicks@xxxxxxxxx>
