This really documented as such.
 
The listserv postmaster must define another minidisk for Listserv's
use.  Next, it is a good idea to add a MDISK.cuu statement to LOCAL SYSVARS,
to have Listserv watch the space usage.
 
When that is done, archiving for a particular list is started by
setting the list keyword NOTEBOOK= Yes,fm,type,access
 
where fm is the filemode of the log disk
      type of archive, most commonly Monthly
      access   who can request the log, usually Public
 
The Notebook keyword is documented in the file LISTKEYW MEMO, while
the MDISK.cuu statement for LOCAL SYSVARS is documented within LOCAL SYSVARS.