RMAN Database Clone

Question

When cloning a database with RMAN do all the old datafiles, control files and redo logs need to be removed or will Oracle overwrite these files
with the backup ? I seen some documention that says to remove the old files first.
Thanks

Answer 1

user771256 wrote:
So what your saying using the same number of datafiles and same file names just keep them all in the same directory including control files and redo logs etc..
Does it wipe the whole file clean first then re-write the file. This database is 500GB and I do this often for our test enviroment.
If seems like this would make more work for Oracle to do.
What happens to the datafile if its larger then what is being restored ?
Does Oracle clean out the old data blocks in each datafile during the clone process ?
Thanks-I'd bet a round at the local pub that rman is simply asking the OS to open the file for output, then asking the os to write to said file, passing it the blocks to be written. Point being that rman itself is not really writing the file, but asking the OS to do it with standard I/O calls to the OS. And I believe that if the OS is asked to open a file for output, and a file with that name already exists, the OS will simply de-allocate the space occupied by the existing file, then start allocating space by its normal mechanism, having no bearing on where the pieces of the original file were located.
So the answer would be no it does not wipe the old file (at least not in the sense of preserving the space but deleting the contents), it simply deallocates the space that it occupied. And then starts allocating space for the new file, with said space may or may not include all or parts of the space previously occupied by the old file.