Um estudo comparativo entre Journaling e Copy-on-Write em sistemas de arquivos

Abstract

The reliability of file systems depends on mechanisms capable of preserving data consistency in the presence of abrupt failures. Among the main approaches adopted are Journaling and Copy-on-Write (CoW), which follow distinct strategies to achieve this goal. This work presents a comparative analysis of these techniques, exploring their conceptual foundations and practical implementations. Journaling is examined through the Ext4 file system, highlighting the role of JBD2 in the organization of transactions, commits, and recovery after failures. In contrast, Copy-on-Write is studied based on OpenZFS, where immutable block writes and the use of atomic commits ensure structural consistency. The comparison shows that journaling preserves the traditional file system architecture by adding a protection log, whereas CoW redefines the system’s internal design, enabling advanced functionalities such as snapshots and clones.