All Oracle RAC instances must be able to access all data files. If a data file must be recovered when the database is opened, then the first Oracle RAC instance to start is the instance that performs the recovery and verifies access to the file. As other instances start, they also verify their access to the data files. Similarly, when you add a tablespace or data file or bring a tablespace or data file online, all instances verify access to the file or files.
If you add a data file to a disk that other instances cannot access, then verification fails. Verification also fails if instances access different copies of the same data file. If verification fails for any instance, then diagnose and fix the problem. Then run the ALTER SYSTEM CHECK DATAFILES statement on each instance to verify data file access.