Oracle backup fails with error "RMAN-06056: could not access datafile".

Make the datafile accessible or skip it. A backup failure can occur for many reasons. To potentially resolve the issue, understanding the error code is important.
Following are the list of error code along with the reason.

The specified datafile could not be accessed. The reason codes are:

 1 - filename is MISSINGxx in the controlfile
 2 - file is offline
 3 - file is not verified
 4 - DBWR could not find the file
 5 - unable to open file
 6 - I/O error during read
 7 - file header is corrupt
 8 - file is not a datafile
 9 - file does not belong to this database
10 -file number is incorrect
12 -wrong file version
15 -controlfile is not current

Check the status of the datafile and take action as per the reason for the error code. This would require sound knowledge and understanding of ORACLE database operations and RMAN, so Veritas recommends to contact ORACLE support if necessary.

How to check the status of the datafile.

1. Connect to the Oracle database using sqlplus tool
2. Run the following command
  select file#, status, enabled from v$datafile where file# = XXX;

Note: XXX is the datafile number that will be reported in the job log.


Please refer to this following link to find the cause and neccessary action to resolve the RMAN issues.

    https://tahiti.oracle.com/pls/db92/db92.error_search?search=%25s