Library /sys$common/syshlp/scacp$help.hlb START, TRACE, Qualifiers, /SIZE  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /SIZE[=n]

    Specifies a trace buffer size of n bytes to be used by PEDRIVER
    for each trace buffer: one for global PEDRIVER use, one for each
    selected channel, and one for each selected VC.