In a two-server dataguard setup, can I store the recovery catalog in the same database? We currently have an Oracle 11gR2 database that is backed up with rman, with the rman records stored in the control files. Control file auto-backup is turned on. Backups are to disk (and, ultimately, via Bacula, to more disks and to tape, but rman doesn't know this).

I'm planning on adding a physical standby database using Data Guard Redo Apply. The Data Guard and and RMAN documents all tell me that I must use a recovery catalog now. I don't actually, so far as I can tell need any of the features of a recovery catalog. The control file was fine. I don't need to offload backup from the primary database; it has more than enough capacity to do them itself (and the workload basically guarantees that will always be the case).

So, I would just put it in the same database (the one I'm backing up with rman), but those same documents tell me I mustn't, but they only reason I've found so far is:


  To illustrate why data separation is advised, assume that you store the catalog for database prod1 in prod1. If prod1 suffers a total media failure, and if the recovery catalog for prod1 is also stored in prod1, then if you lose the database you also lose the recovery catalog.


But this isn't true. The recovery catalog would still exist on the standby. And even if both the primary and standby broke simultaneously (say, due to a madman at a sqlplus prompt, but that'd break a recovery catalog in a separate database, too), they say:


  At this point the only option is to restore an autobackup of the control file for prod1 and use it to restore and recover the database without the benefit of any information stored in the recovery catalog. ("Protecting the Recovery Catalog" from Oracle Database Backup and Recovery User’s Guide 11g Release 2 (11.2), p. 13-15.)


The "only option" of using a control file backup doesn't sound bad at all.

Am I missing something? Are there some non-obvious downsides to putting the recovery catalog in the same database, or is this really only a concern in a much larger operation?

(would tag this recovery-catalog and data-guard as well, but seems I can't with less than 300 rep here)
If I correctly understand your question as: "I want to create a standby database and later on take backups on the primary like if there would be no standby present"

In this case, you do not need a recovery catalog: quote "An RMAN recovery catalog is required so that backups taken on one database server can be restored to another database server. It is not sufficient to use only the control file as the RMAN repository because the primary database will have no knowledge of backups taken on the standby database." See http://download.oracle.com/docs/cd/E11882_01/server.112/e25608/rman.htm#BAJEDHFB