Filesystem Fragmentation on Modern Storage Systems

Filesystem fragmentation has been one of the primary reasons for computer systems to get slower over time. However, there have been rapid changes in modern storage systems over the past decades, and modern storage devices such as solid state drives have different mechanisms to access data, compared with traditional rotational ones. In this paper, we revisit filesystem fragmentation on modern computer systems from both performance and fairness perspectives. According to our extensive experiments, filesystem fragmentation not only degrades I/O performance of modern storage devices, but also incurs various problems related to I/O fairness, such as performance interference. Unfortunately, conventional defragmentation tools are designed primarily for hard disk drives and thus generate an unnecessarily large amount of I/Os for data migration. To mitigate such problems, this paper present FragPicker, a new defragmentation tool for modern storage devices. FragPicker analyzes the I/O behaviors of each target application and defragments only necessary pieces of data whose migration can contribute to performance improvement, thereby effectively minimizing the I/O amount for defragmentation. Our evaluation with YCSB workload-C shows FragPicker reduces the total amount of I/O for defragmentation by around 66% and the elapsed time by around 84%, while showing a similar level of defragmentation effect.