单机需要更改redo log大小，如何加入： 

ALTER DATABASE ADD LOGFILE GROUP 4 ('/u01/product/mxdell/redo04a.log')   SIZE 100m;
ALTER DATABASE ADD LOGFILE GROUP 5 ('/u01/product/mxdell/redo05a.log')   SIZE 100m;
ALTER DATABASE ADD LOGFILE GROUP 6 ('/u01/product/mxdell/redo06a.log')   SIZE 100m;
ALTER DATABASE ADD LOGFILE GROUP 7 ('/u01/product/mxdell/redo07a.log')   SIZE 100m;
ALTER DATABASE ADD LOGFILE GROUP 8 ('/u01/product/mxdell/redo08a.log')   SIZE 100m;
ALTER DATABASE ADD LOGFILE GROUP 9 ('/u01/product/mxdell/redo09a.log')   SIZE 100m;

ALTER system switch logfile;
ALTER system switch logfile;
ALTER system switch logfile;
ALTER system switch logfile;

ALTER DATABASE DROP LOGFILE GROUP 1;
ALTER DATABASE DROP LOGFILE GROUP 2;
ALTER DATABASE DROP LOGFILE GROUP 3;  

SQL> alter database add logfile thread 2
     group 4   (‘/oradata1/rac/redo04.log’) size 102400k ,
     group 5   (‘/oradata1/rac/redo05.log’) size 102400k ,
     group 6   (‘/oradata1/rac/redo06.log’) size 102400k ;

SQL>alter database open ;

SQL>alter database enable public thread 2 ;

ALTER system switch logfile;
ALTER system switch logfile;
ALTER system switch logfile;
ALTER system switch logfile;

ALTER DATABASE DROP LOGFILE GROUP 1;
ALTER DATABASE DROP LOGFILE GROUP 2;
ALTER DATABASE DROP LOGFILE GROUP 3;