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

    (Alpha only) The dynamic system parameter VCC_READAHEAD controls
    whether the Extended File Cache can use read-ahead caching. Read-
    ahead caching is a technique that improves the performance of
    applications that read data sequentially.

    By default VCC_READAHEAD is 1, which means that the Extended File
    Cache can use read-ahead caching. The Extended File Cache detects
    when a file is being read sequentially in equal-sized I/Os, and
    fetches data ahead of the current read, so that the next read
    instruction can be satisfied from cache.

    To stop the Extended File Cache from using read-ahead caching,
    set VCC_READAHEAD to 0.

    Changing the value of VCC_READAHEAD affects volumes currently
    mounted on the local node, as well as volumes mounted in the
    future.

    Readahead I/Os are totally asynchronous from user I/Os and only
    take place if sufficient system resources are available.

    VCC_READAHEAD is a DYNAMIC parameter.