In the Block Size list, enter the size in bytes or accept the default. Oracle Database data is stored in these blocks. One data block corresponds to a specific number of bytes of physical space on disk. While using pre-defined templates, this field is not enabled since the database will be created with the default block size of 8 KB. But while using the custom option, you can change block size. Selecting a block size other than the default 8 KB value requires advanced knowledge and should only be done when absolutely required. docs.oracle.com/cd/B16351_01/doc/server.102/b14196...
Уверен, вы точно знаете зачем вам нестандартный размер блока ;)