When Oracle ASM creates a data file for a permanent tablespace (or a temporary file for a temporary tablespace), the data file is set to auto-extensible with an unlimited maximum size and 100 MB default size. You can use the AUTOEXTEND clause to override this default extensibility and the SIZE clause to override the default size.
Oracle ASM applies attributes to the data file, as specified in the system default template for a data file as shown in the table in "Managing Disk Group Templates". You can also create and specify your own template.
Files in a tablespace might be in both Oracle ASM files and non-Oracle ASM files due to the tablespace history. RMAN commands enable non-Oracle ASM files to be relocated to an Oracle ASM disk group and enable Oracle ASM files to be relocated as non-Oracle ASM files.
For example, if there is a disk group named data, then you can create a tablespace tblspace in that disk group with the following SQL statement:
SQL> CREATE TABLESPACE tblspace DATAFILE '+data';
The following example illustrates the usage of Oracle ASM with defaults. This example enables Oracle ASM to create and manage the tablespace data file for you, using Oracle supplied defaults that are adequate for most situations.
Assume the following initialization parameter setting:
DB_CREATE_FILE_DEST = +data
The following statement creates the tablespace and its data file:
SQL> CREATE TABLESPACE tblspace;