Environment: Windows 2003, Oracle 10gR2, 2 node RAC with ASM and multiple databases

Is setting Automatic Memory Management (by setting parameter SGA_TARGET greater than zero) for ASM instance a good thing or not.

Do we have lot of overhead in using Automatic Memory Management, especially for instances that have a low amount of memory allocated. Does Oracle spend more time moving memory allocations back and forth between the pools than doing any real work.

We have about 20 databases running on RAC for that ASM instance.