Oracle 11g: increasing buffer cache with AMM On a 2-node RAC we have enabled Automatic Memory Management. The advisor views indicate that increasing the buffer cache by 4 GB will half the physical reads, and we have 4 GB to give. 

How must we do this? By increasing memory_target and letting Oracle grab more memory for the buffer cache? Or by explicitly setting a value for db_cache_size (which now is zero)?
You can set the value for db_cache_size, and the value you set for it will be considered the minimum value it can be with AMM enabled.