The note ebrian suggested is a good one... please note something though... the steps in the note assumes you are using the Enterprise Edition of the database.
The command CONFIGURE DEVICE TYPE disk PARALLELISM <# of instances> is not valid for the Standard Edition. We found this out the hard way... I am at a client location and couldn't figure out why RMAN had a hard time finding all backups. The issue is that when RMAN runs, it is just like any other client the RAC database and the db will determine which instance you are actually connected to... If you are creating a backup in RMAN in this fashion, you never really know on which local file system the backup files will be located.
If you don't have EE (which we will continue to "NOT" have) you will have to create some custom backup scripts. Something like this:
CONFIGURE CHANNEL DEVICE TYPE disk CONNECT 'sys/pwd@inst1'
BACKUP DATABASE PLUS ARCHIVELOG;
This will ensure that the files are stored on the instance you determine... In our case, as a "backup" to this process, we duplicated our backup scripts to run on both instances -- it has the added benefit of creating a backup copy.
Hope this helps... and if you find another solution, please share.
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