Complex sentence: In a log-structured filesystem, rather than being a conventional filesystem with an added journal log, the journal log itself is used as the fundamental basis for the filesystem, meaning that both filesystem meta-data and the filesystem data are journaled.
Split into simpler sentences: In a log-structured filesystem, rather than being a conventional filesystem with an added journal log, the journal log itself is used as the fundamental basis for the filesystem. Meaning that both filesystem meta-data and the filesystem data are journaled.