What is the data layout of an RMAN file?

Question

I would like to know the on disk format of an RMAN backup file. Is this documented anywhere?

Answer 1

The RMAN backup file format is not documented anywhere, may be different in different versions, and it is subject to change at any point.

Why do you want to know how to read an RMAN backup? An RMAN backup is really only intended to be useful to RMAN so that it can do a restore.

Writing software to parse the file and extract the information from it is probably not a practical way forward unless you're willing to invest at least a few thousand man-hours. The format is likely to be relatively similar to the format of a data file with some additional RMAN-specific stuff tacked on. There is one group outside of Oracle that has done a pile of work on the format of an Oracle data file so that they could write DUDE, a last-ditch Oracle recovery tool. These folks charge an arm and a leg for their tool (though less than Oracle charges for their version of the same tool) and there is always a demand from people that have unrecoverable databases that want to extract whatever data they can salvage. If you could reverse engineer the data file format in hundreds of man-hours rather than thousands, there would be dozens of competitors in this space.