Library /sys$common/syshlp/tracehlp.hlb START, /BLOCKS  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    /BLOCKS=n

    The approximate size (in blocks) of each  output  file.   Once  the
    file reaches this size it is closed and a new one created.

    The default value is 200.

    Not valid with /LIVE qualifier.