CassandraHardware - Cassandra WikiMemory The most recently written data resides in memory tables (aka memtables), but older data that has been flushed to disk can be kept in the OS's file-system cache. In other words, the more memory, the better, with 4GB being the minimum we typically recommended in a virtualized environment (e.g., EC2 Large instances). Obviously there is no benefit to having more RAM than your hot data set, but
