RMAN controlfile autobackup takes too long

Hi.
I'm using RMAN (11.1.0.7 on Oracle Enterprise Linux 5.6) to backup DB to Oracle Secure Backup (via SBT channel). My script is very simple:

CONFIGURE RETENTION POLICY TO REDUNDANCY 2;
LIST BACKUP SUMMARY DEVICE TYPE 'sbt';
REPORT OBSOLETE DEVICE TYPE 'sbt';
ALLOCATE CHANNEL FOR MAINTENANCE DEVICE TYPE sbt;
DELETE NOPROMPT OBSOLETE DEVICE TYPE='sbt';
RELEASE CHANNEL;
LIST BACKUP SUMMARY DEVICE TYPE 'sbt';
run {
   allocate channel C1 device type sbt;
   backup filesperset 4 incremental level 0 database;
   sql "alter system switch logfile";
   backup archivelog all delete all input;
   backup current controlfile;
   release channel C1;
}

rman shows this configuration:
CONFIGURE RETENTION POLICY TO REDUNDANCY 2;
CONFIGURE BACKUP OPTIMIZATION OFF; # default