RMAN : Duplicate database without connecting to target

Using "backup location", I do not need to connect to target database, but how do I know what "until time" is available in the backup pieces? one way is to find the backup piece information from target database by using "list backup...", but what if I do not have the target database at all? while, I can arbitrarily give a time, then RMAN will tell me what is the time in those back pieces, nice!

Steps captured!

1.create the RAC database using dbca
2.create spfile='+oradata/bcfw/spfileBCFW.ora' from pfile='/tmp/pfile.ora'. 
   alter system set cluster_database=false scope=memory
3.srvctl start instance -d dbname -i dbname1 -o nomount
4.export NLS_DATE_FORMAT='yyyymmdd hh24:mi:ss'
5.rman> duplicate database
/* the backup was done using this:
RUN
{
  ALLOCATE CHANNEL ch11 TYPE DISK MAXPIECESIZE 1G;
  BACKUP as COMPRESSED backupset
  FORMAT '/u01/dba/jsun/%d_D_%T_%u_s%s_p%p'
  DATABASE
  PLUS ARCHIVELOG
  FORMAT '/u01/dba/jsun/%d_A_%T_%u_s%s_p%p';
  RELEASE CHANNEL ch11;
 }
*/

Duplicate database:
Method 1: get the until scn from target database.

export NLS_DATE_FORMAT='yyyymmdd hh24:mi:ss'
rman>
 list archivelog time between 'sysdate-1' and 'sysdate';
 list backup of archivelog time between 'sysdate-1' and 'sysdate';

On auxiliary database:
connect auxiliary  /
connect target sys/syspassword@targetdb
RUN
{
  ALLOCATE auxiliary  CHANNEL ch11 TYPE DISK MAXPIECESIZE 1G;
  set until scn 9776681621703;
  duplicate target database to 'BCFW' NOFILENAMECHECK;
  RELEASE   CHANNEL ch11;
 }

Method 2: replicate database using backup location without connecting to target database

export NLS_DATE_FORMAT='yyyymmdd hh24:mi:ss'
connect auxiliary  /
RUN
{
  ALLOCATE auxiliary  CHANNEL ch11 TYPE DISK MAXPIECESIZE 1G;
  duplicate database to 'BCFW' NOFILENAMECHECK until time "to_date('04-04-2019 13:31:18','dd-mm-yyyy hh24:mi:ss')" backup location '/u01/dba/jsun';
  RELEASE   CHANNEL ch11;
}

Errors in memory script
RMAN-06617: UNTIL TIME (20190404:13:31:18) is ahead of last NEXT TIME in archived logs (20190404:10:56:44)

Bingo! Now we get the correct time from the error 20190404:10:56:44

RUN
{
  ALLOCATE auxiliary  CHANNEL ch11 TYPE DISK MAXPIECESIZE 1G;
  duplicate database to 'BCFW' NOFILENAMECHECK until time "to_date('04-04-2019 10:56:44','dd-mm-yyyy hh24:mi:ss')" backup location '/u01/dba/jsun';
  RELEASE   CHANNEL ch11;
}

The duplicating database finish successfully!

6.
alter system set cluster_database=true scope=spfile;
select group#,member,status from gv$logfile;
select group#,thread#,bytes,status from gv$log;
alter database drop logfile group 21; ---... there are redundant redo groups.
alter database add logfile thread 2 group 4 ('+oraDATA01','+oraFLASH01') size 524288000 reuse;
alter database add logfile thread 2 group 5 ('+oraDATA01','+oraFLASH01') size 524288000 reuse;
alter database add logfile thread 2 group 6 ('+oraDATA01','+oraFLASH01') size 524288000 reuse;
alter database add logfile thread 3 group 7 ('+oraDATA01','+oraFLASH01') size 524288000 reuse;
alter database add logfile thread 3 group 8 ('+oraDATA01','+oraFLASH01') size 524288000 reuse;
alter database add logfile thread 3 group 9 ('+oraDATA01','+oraFLASH01') size 524288000 reuse;
alter database enable public thread 2;
alter database enable public thread 3;
show parameter undo
show parameter spfile; if you are using wrong spfile, correct that.
create pfile='/u01/dba/jsun/d' from spfile;  -- theck the parameters and make sure they are correct
select tablespace_name,file_name, bytes,autoextensible from dba_data_files where tablespace_name like '%UNDO%';
drop tablespace undotbs5; ... --- there are redundant undo...
#create undo tablespace UNDOTBS2 datafile  '+oraDATA01' size 500M;

7. srvctl start database -d BCFW; srvctl status database -d BCFW
8. srvctl add service -d BCFW -s BCFW_TAF -r "BCFW1,BCFW2,BCFW3"
srvctl modify service -d BCFW -s BCFW_TAF -e SELECT -m BASIC  -z 5 -w 0
/* options for srvctl modify service
 -P {NONE | BASIC | PRECONNECT} TAF policy specification
 -l <role> Role of the service (primary, physical_standby, logical_standby, snapshot_standby)
 -y <policy> Management policy for the service (AUTOMATIC or MANUAL)
 -e <Failover type> Failover type (NONE, SESSION, or SELECT)
 -m <Failover method> Failover method (NONE or BASIC)
 -w <integer> Failover delay
 -z <integer> Failover retries
*/