Does only the metadata get journalled in ext3 or does the data get journalled too?
From the mount manpage:
Specifies the journalling mode for file data. Metadata is always journaled. To use modes other than ordered on the root filesystem, pass the mode to the kernel as boot parameter, e.g. rootflags=data=journal.
All data is committed into the journal prior to being written into the main filesystem.
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.
Data ordering is not preserved - data may be written into the main filesystem after its metadata has been committed to the journal. This is rumoured to be the highest-throughput option. It guarantees internal filesystem integrity, however it can allow old data to appear in files after a crash and journal recovery.
By default only metadata, with the data=journal mount option, both data and metadata.
You get to choose, with a mount option. By default, it is metadata only.