Considerations for Disk Based Dictionary Structures
Use a disk-based method when the dictionary is too big to fit in RAM at once.
Minimize the expected or worst-case number of disk accesses for the essential operations (put, get, remove).
Keep space requirements reasonable -- O(n).
Methods based on binary trees, such as AVL search trees, are not optimal for disk-based representations. The number of disk accesses can be greatly reduced by using m-way search trees.