我的回滚段创建不成功为什么？

创建语句如下：
CREATE TABLESPACE RBS DATAFILE '/dbs/8i/oradata/ora8/rbs01.dbf' SIZE 516M REUSE
AUTOEXTEND ON NEXT 2m
MINIMUM EXTENT 2m
DEFAULT STORAGE(INITIAL 2m NEXT 2m MINEXTENTS 20 MAXEXTENTS 4096);


错误如下：
SVRMGR> SVRMGR> SVRMGR> CREATE PUBLIC ROLLBACK SEGMENT RBS0 TABLESPACE RBS STORAGE ( OPTIMAL 2m )
*
ORA-01593: rollback segment optimal size (512 blks) is smaller than the computed initial size (10240 blks)
SVRMGR> CREATE PUBLIC ROLLBACK SEGMENT RBS1 TABLESPACE RBS STORAGE ( OPTIMAL 2m )