I finally found the issue with my migrated database. It's a bug - it prevents RMAN compressed backups made with a 6k blocksize from being usable. Yup, my backups were completely unusable. Thank goodness I discovered that BEFORE needing a backup.
I'm not going to reproduce the text of the bug. Its Bug ID is 9789190 - you can look it up.
The bug describes it as compressed backups created using an 'unusual' block size. Well, OK, is 6k an unusual block size? I thought in 9i it was pretty common. It's been fixed in 11.2.0.1, it definitely affects 10.2.0.5 & 10.2.0.4.
I discovered it by accident. After converting the training db, I backed it up, and then messed around, then restored it. It didn't restore. I wasn't concerned about the restore per se, since I still had the offline backup from the 9i db. But, I was concerned that a freshly baked backup didn't work. That's how I found this bug. I was not a happy bunny when I found it, since that customer's live db has the same problem.
But, there are workarounds if you discover this issue the easy way. Don't use compressed backups or don't use an 'unusual' blocksize. Sigh.
I tested the use of uncompressed RMAN backups, and yes, that works. I would also say that the standard Export I would also highly recommend in such circumstances.
In a separate blog I'll detail how I'm going to deal with this permanently.
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