Aging resistance of file systems under near-full-disk conditions

Determine whether BetrFS or any other file system can avoid aging—defined in the paper as performance degradation due to fragmentation and poor on-disk layout—under near-full-disk conditions, and ascertain the circumstances under which aging can be prevented when storage devices operate with very limited free space.

Background

The paper demonstrates that many production file systems experience significant read aging due to fragmentation even when devices are nearly empty, whereas BetrFS—a Be-tree-based, write-optimized research file system—shows minimal aging in such scenarios. However, when the device is near full, BetrFS became unstable and could not complete the test suite, prompting the authors to raise an explicit open question about aging resistance in that regime.

This problem sits at the intersection of allocation strategies, fragmentation dynamics (intra-file, inter-file, and free-space), and space pressure. Establishing whether any file system design, including write-optimized approaches like BetrFS, can sustain locality and avoid aging when free space is scarce would clarify the limits of current techniques and inform future file-system architectures and defragmentation policies.