In a white paper talking about Oracle RMAN Design Best Practices for Data Domain there is mention of RMAN encrypted backups as being not optimal for Data Domain. There is this one sentence though:
When a backup of otherwise unchanged data is muliplexed, compressed, or encrypted on the fly, the resultant data stream is different each time.
That implies that data at rest that is encrypted, as in Oracle Transparent Data Encryption, could still be a candidate for Data Domain since it is encrypted on the disk before transported and not encrypted on the fly.
Thus, It seems that using Oracle Advanced Compression or Oracle Transparent Data Encryption would still allow Data Domain's deduplication to work.
Can anyone provide more details on whether this is true?