The IOs from the client for Oracle databases are NFS reads and writes. Within the Delphix Engine, these NFS IOs may be translated into physical IOs of a different size but this detail is not visible to the database client. The underlying physical IO sizes have been optimized within the Delphix Engine according to file type. For Oracle data files, the underlying filesystem block size is set to the database block size.
Therefore, Delphix will use a size based upon the db_block_size specified in the database.
I hope this helps. Please let me know if you have any questions.