The root directory is the base directory in the volume. The root directory of a volume typically contains only directories.
Storing files at this level is possible, but it can be a security risk. Granting file-system trustee rights to files at the root of the volume necessitates granting rights to the entire volume. For information about trustee rights, see Understanding File System Access Control Using Trustees.
To avoid this security risk, create Fake Roots for applications that want to write files to the root directory. For information, see Section 5.4, Fake Root Directory.