I have cluster of 3 cassandra 0.7.3 nodes, and some times nodes a frozen. As i understand this because GC, in this moment i see

INFO [ScheduledTasks:1] 2011-03-05 15:21:23,524 GCInspector.java (line 128) GC for ConcurrentMarkSweep: 18052 ms, -997761672 reclaimed leaving 5796586088

How can i reduce this? I installed JNA (i install it correctly: "CLibrary.java (line 106) JNA mlockall successful" log record  in system.log present on all nodes), and set vm.swappiness = 0, but this doesn't help. Any suggest?

PS: Nodes have 12GB of memory with 6GB HeapSize