The cache block size is the size of each memory block used for caching, the only two options are 4k and 16k. The cache block size should be set to the size of the average work unit, or less. Never exceed the size of the average work unit. For instance, if you are using Oracle with an 8k segment size, you should use 4k. Using 16k will result in each cache block only bing half utilized. Using 4k will use two blocks, but they will both be filled. This can be changed under Storage Subsystem -> Change -> Cache Settings.