icm/HTTP/server_cache_<xx>/memory_size_MB 

The size of the entire cache is set by the parameter icm/HTTP/server_cache_<xx>/size_MB.

In other words, this parameter decides which part of the cache should be stored in main memory and which on the hard disk.

If sufficient main memory is available, this parameter should be set to a high value, to ensure maximum performance.

For a rule of thumb for dimensioning, see the parameter documentation under icm/HTTP/server_cache_<xx>/size_MB.