Ext3 works in several modes: writeback, journal, and ordered, which log respectively, metadata-only, both data and metadata, or something in between. (Ext3 FAQ). So at least with ext3, it is posible to protect data in addition to metadata, but it seems like this is already being accomplised with WAL.
So using a journaling fs may not give me additional coverage over the write-ahead log, but I'm still inclined to use it so that I can avoid a costly fsck on my data partition. However, now there is the issue Roberto raised about potential double-logging if you try to use both. It seems odd that my decision to use a journaling fs on a partition would depend on whether or not an application writing to that partition has its own journaling method. I'll have to think about that more.
