Типы журналов Ext3

journal
All data is committed into the journal prior to being written into the main file system.

ordered
This is the default mode. All data is forced directly out to the main file system prior to its metadata being committed to the journal.

writeback
Data ordering is not preserved - data may be written into the main file system after its metadata has been committed to the journal. This is rumoured to be the highest-throughput option. It guarantees internal file system integrity, however it can allow old data to appear in files after a crash and journal recovery.

А вот информация прямиком из ядра (filesystems/ext3.txt):

journal All data are committed into the journal prior to being written into the main file system.

ordered (*) All data are forced directly out to the main file system prior to its metadata being committed to the journal.

writeback Data ordering is not preserved, data may be written into the main file system after its metadata has been committed to the journal.

И еще немного с документации ядра:

* writeback mode
In data=writeback mode, ext3 does not journal data at all. This mode provides
a similar level of journaling as that of 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 performs 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
outperforms all other modes.