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

    MPW_WRTCLUSTER sets the number of pages to be written during one
    I/O operation from the modified-page list to the page file or
    a section file. The actual size of the cluster may be limited
    by the number of pages available for the I/O operation. This
    parameter can range in value from 16 to 120, in multiples of 8.
    Each page in the cluster requires 6 bytes of permanently resident
    memory.

    If MPW_WRTCLUSTER is too small, it takes many I/O operations
    to empty the modified-page list. If MPW_WRTCLUSTER is too large
    for the speed of the disk that holds the page file, other I/O
    operations are held up for the modified-page list write.

    On VAX systems, the MPW_WRTCLUSTER default value and maximum
    value is 120 512-byte pages; its minimum value is 16 512-byte
    pages.

    On Alpha systems, the MPW_WRTCLUSTER default value is 64 8192-
    byte pages; its maximum value is 512 8192-byte pages; and its
    minimum value is 16 8192-byte pages.

    MPW_WRTCLUSTER has the AUTOGEN and GEN attributes.