Database Software

Using Oracle 10g R2. I am trying to set up a tape backup with 2 copies in a highly available environment. The media management software (IBM TDP for Oracle) is configured so that the copies are written to separate tape libraries. If one of the libraries is unavailable for some reason, I would like the other copy to complete, even if the first one has failed. I have disabled the first library for testing purposes and ran RMAN (transcript follows):

RMAN> run {
2> set backup copies = 2;
3> allocate channel t1 type 'sbt_tape' parms 'ENV=(TDPO_OPTFILE=/opt/tivoli/tsm/config/tdpo.opt)';
4> backup format 'backupset_%s.copy_%c' database;
5> release channel t1;
6> }
executing command: SET BACKUP COPIES
using target database control file instead of recovery catalog

allocated channel: t1
channel t1: sid=46 devtype=SBT_TAPE
channel t1: Data Protection for Oracle: version 5.4.1.0

Starting backup at 23-MAY-07
channel t1: starting full datafile backupset
channel t1: specifying datafile(s) in backupset
input datafile fno=00004 name=/mnt/sda6/oracle/users.dbf
input datafile fno=00001 name=/mnt/sda6/oracle/system.dbf
input datafile fno=00003 name=/mnt/sda6/oracle/sysaux.dbf
input datafile fno=00002 name=/mnt/sda6/oracle/undotbs.dbf
channel t1: starting piece 1 at 23-MAY-07
released channel: t1
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03009: failure of backup command on t1 channel at 05/23/2007 16:19:17
ORA-19502: write error on file "backupset_13.copy_1", blockno 52737 (blocksize=512)
ORA-27030: skgfwrt: sbtwrite2 returned error
ORA-19511: Error received from media manager layer, error text:
ANS1312E (RC12) Server media mount not possible

RMAN> **end-of-file**

The "media mount not possible" error results from the first library being disabled. The second library, however, is available. It seems that RMAN just drops the entire session instead of writing the second copy to the second library. Is there any way to achieve this?

Thanks in advance