Recently I tinkered around with RMAN to see how it works, and somehow managed to get a regularly scheduled backup going. I don't really have the disk space or the need for RMAN to run, but I can't figure out how to stop it from creating backup sets. I think the original commands I used were:
$ rman target=/
RMAN> configure retention policy to redundancy 2;
RMAN> configure controlfile autobackup on;
RMAN> backup database plus archivelog delete input;
From what I can see, the job that has been scheduled is the automatic backup of the controlfile. That shouldn't eat up a lot of space, but you should be able to turn that off with:
RMAN will only work if you tell him to. It doesn't have any scheduler. The autobackup of the control files isn't done on a regular basis but on response to some events ( see the documentation ) and should not cause disk issues (a control file weights only some megabytes).
You must have something scheduled, using Enterprise Manager, the Oracle DBMS_SCHEDULER and DBMS_JOB packages or the system scheduler.