Hope you have read

• Journaling File System in Linux
• Copy-on-write Filesystem in Linux in a Nutshell

This comparison table is taken from the book “Architecture and Design of the Linux Storage Stack” which I find useful to help understand the differences between the two.

	Journaling	Copy-On-Write
Write handling	Changes are recorded in a journal before applying them to the actual file system	A separate copy of data is created to make modifications
Original data	Original data gets overwritten	Original data remains intact
Data Consistency	Ensures consistency by recording metadata changes and replaying them if needed	Ensures consistency by never modifying the original data
Performance	Minimal overhead depending on the type of journaling mode	Some performance gains because of faster writes
Space utilisation	Journal size is typically in MB, so no additional space is required	More space is required due to separate copies of data
Recovery times	Fast recovery times as the journal can be replaced instantly	Slower recovery times as data needs to be reconstructed using recent copies
Features	No built-in support for features such as compression or deduplication	Built-in support for compression and deduplication