With DECC$EFS_CASE_PRESERVE enabled, case is preserved for
    filenames on ODS-5 disks.

    With DECC$EFS_CASE_PRESERVE disabled, UNIX style filenames are
    always reported in lowercase.

    However, note that enabling DECC$EFS_CASE_SPECIAL overrides the
    setting for DECC$EFS_CASE_PRESERVE.