VMS Help Sys Parameters, VCC_MAX_CACHE  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    (Alpha only) The dynamic system parameter VCC_MAX_CACHE controls
    the maximum size of the Extended File Cache. It specifies the
    size in megabytes. By default, VCC_MAX_CACHE has a special value
    of -1 for people who do not want to tune their systems manually;
    this value means that at system startup, the maximum size of the
    Extended File Cache is set to 50 percent of the physical memory
    on the system.

    The Extended File Cache can automatically shrink and grow,
    depending on your I/O workload and how much spare memory
    your system has. As your I/O workload increases, the cache
    automatically grows, but never to more than the maximum size.
    When your application needs memory, the cache automatically
    shrinks.

    The value of VCC_MAX_CACHE at system startup sets an upper limit
    for the maximum size of the Extended File Cache. You cannot
    increase the maximum size of VCC_MAX_CACHE beyond its value
    at boot time. For example, if VCC_MAX_CACHE is 60 MB at system
    startup, you can then set VCC_MAX_CACHE to 40, which decreases
    the maximum size to 40 MB. If you then set VCC_MAX_CACHE to 80,
    the maximum size is only increased to 60 MB, the value set at
    system startup.

    Note that VCC_MAX_CACHE is a semi-dynamic parameter. If you
    change its value, you must enter the DCL command SET CACHE/RESET
    for any changes to take effect immediately. Otherwise, it might
    take much more time for the changes to take effect.

    If you are using the reserved memory registry to allocate
    memory permanently, you must set the VCC$MIN_CACHE_SIZE entry
    in the reserved memory registry to a value less than or equal to
    VCC_MAX_CACHE at system startup time.

    Refer to the OpenVMS System Manager's Manual for instructions on
    setting permanent memory allocations for the cache.

    VCC_MAX_CACHE is a DYNAMIC parameter.