I would also consider separating Directories and Files into their own tables.
I'll suggest against putting those into their own tables. It would be like putting managers and employees in their own tables, which pretty much screws the whole notion of the hierarchy.
If you have the files and directories in the same table, then you can also use the method in the article at the second link to get byte totals for all levels of all directories.
I see Managers and Employees as both being Employees, therefor keeping 1 table, with an EmployeeType field.
However, I see Directories and Files as completely separate entities, hence the normalisation.
That said, the ability to get to the byte totals would be a compelling reason to demormalise in this case.