Try this, it's from my AIX notes but should work..

DSMFMT an additional recovery log volume:

dsmfmt -m -log temprec1.log01 101

Use the DSMSERV EXTEND LOG command to do a recovery log extension:

dsmserv extend log temprec.log01 100

Start the TSM server. When it comes up login and disable sessions, cancel
all current sessions, and cancel all processes that may be running. Start an
incremental backup.

Once your backup is complete and the log percent utilized drops, if in
rollfoward set the log mode to normal:

set logmode normal

Then reduce the log size and delete the new log volume:

reduce log 100
delete logvol temprec.log01

Set logmode back to roll forward:
set logmode rollfoward