ACP_WRITEBACK

   ACP_WRITEBACK is a dynamic system parameter that controls whether
   deferred writes to file headers are enabled. The default value is
   1, which enables deferred writes to file headers. To disable the
   feature, set ACP_WRITEBACK to 0.

   This system parameter affects only applications like PATHWORKS
   that can request deferred writes to file headers. Note that
   the deferred write feature is not available on Files-11 ODS-1
   volumes.

   ACP_WRITEBACK is a DYNAMIC parameter.