A file-management system of a computer operating system transfers a hierarchical set of files. The system generates a histogram of the files' true filesizes, using a non-parametric kernel-density estimation (KDE) procedure to estimate the width of each histogram bin. The system splits the fileset into subsets and generates a second-level histogram to represent the true-filesize distribution of each subset, using the previously estimated kernel width to initialize another KDE procedure for each second-level histogram. The distributions identified by each second-level histogram are used to organize the file transfer into a series of passes, each of which completely transfers a group of files that together fit into the computer's I/O buffer minimal wasted space. A waypoint is set at the beginning of each pass and if the system is interrupted mid-transfer, no file transferred before the most recent waypoint is lost.