The SGA size was 5GB and database was running very fine with no performance issues. we changed to the new server with 16 GB of RAM on AIX 5.3 and we allocated 12 GB for SGA MAX SIZE. and allocated 10GB to shared pool. we are experiencing high paging when running RMAN backup's and even a simpleselect statement takes 2-3 minutes(like select name from v$database). As I allocated this memory to the new server and is in production I am not sure that sga can be a problem.
when we run backup's the disk IO is more and the server is paging.