VMS Help INITIALIZE, Qualifiers, /HEADERS  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /HEADERS=number-of-headers

    Specifies, for disk volumes, the number of file headers to be
    allocated for the index file. The minimum and default value
    is 16. The maximum is the value set with the /MAXIMUM_FILES
    qualifier.

    This qualifier is useful when you want to create a number of
    files and want to streamline the process of allocating space
    for that number of file headers. If you do not specify this
    qualifier, the file system dynamically allocates space as it
    is needed for new headers on the volume.

                                   NOTE

       The default value for the /HEADERS qualifier is generally
       insufficient for ODS-2 disks. To improve performance and
       avoid SYSTEM-F-HEADERFULL errors, Compaq recommends that
       you set this value to be approximately the number of files
       that you anticipate having on your disk; however, grossly
       overestimating this value will result in wasted disk space.

    The /HEADERS qualifier controls how much space is initially
    allocated to INDEXF.SYS for headers. Each file on a disk requires
    at least one file header and each header occupies one block
    within INDEXF.SYS. Files that have many Access Control Entries
    (ACE) or are very fragmented may use more than one header.

    The default value of 16 leaves room for less than 10 files to be
    created before INDEXF.SYS must extend; therefore, try to estimate
    the total number of files that will be created on the disk and
    specify it here. This will improve disk access performance.
    Overestimating the value may lead to wasted disk space. This
    value cannot be changed without reinitializing the volume.

    INDEXF.SYS is limited as to how many times it may extend. When
    the map area in its header (where the retrieval pointers are
    stored) becomes full, file creation fails with the message
    "SYSTEM-W-HEADERFULL."