An Empirical Study of the NTFS Cluster Allocation Behavior Over Time

Abstract

The amount of data to be handled in digital forensic investigations is continuously increasing, while the tools and processes used are not developed accordingly. This especially affects the digital forensic sub-field of file carving. The use of the structuring of stored data induced by the allocation algorithm to increase the efficiency of the forensic process has been independently suggested by Casey and us. Building on that idea we have set up an experiment to study the allocation algorithm of NTFS and its behavior over time from different points of view. This includes if the allocation algorithm behaves the same regardless of Windows version or size of the hard drive, its adherence to the best fit allocation strategy and the distribution of the allocation activity over the available (logical) storage space. Our results show that space is not a factor, but there are differences in the allocation behavior between Windows 7 and Windows 10. The results also show that the allocation strategy favors filling in holes in the already written area instead of claiming the unused space at the end of a partition and that the area with the highest allocation activity is slowly progressing from approximately 10 GiB into a partition towards the end as the disk is filling up.