I don't know if this is available to 3.1 or if it came about in 3.7 but
DSMSERV EXTEND LOG (Emergency Log Extension)
Use this command to extend the size of the recovery log when you need
additional log
space to restart the server. After the server is running, you can do the
following:
v Back up the database, which frees the recovery log space.
v Adjust the size of the recovery log, the database backup trigger full
percentage, or
both to allow for successful future database backups.
Note: Use the DSMFMT utility to format a new recovery log volume.
Syntax
         DSMSERV EXTEND LOG volume_name megabytes