Policies: How to Allocate Files and Directories

With the group structure in place, FFS now has to decide how to place files and directories and associated metadata on disk to improve performance. The basic mantra is simple: keep related stuff together (and its corollary, keep unrelated stuff far apart).

Allocation policy

Thus, to obey the mantra, FFS has to decide what is “related” and place it within the same block group. Conversely, unrelated items should be placed into different block groups. To achieve this end, FFS makes use of a few simple ...