Upgrade to Atomix 2.0.18

Change-Id: I433e8b85d5aad007531c24495dd8298aeef9f79e
diff --git a/core/store/primitives/src/main/java/org/onosproject/store/primitives/impl/StoragePartitionServer.java b/core/store/primitives/src/main/java/org/onosproject/store/primitives/impl/StoragePartitionServer.java
index 1b201cd..eb48f66 100644
--- a/core/store/primitives/src/main/java/org/onosproject/store/primitives/impl/StoragePartitionServer.java
+++ b/core/store/primitives/src/main/java/org/onosproject/store/primitives/impl/StoragePartitionServer.java
@@ -206,8 +206,8 @@
                 .withElectionThreshold(ELECTION_THRESHOLD)
                 .withStorage(RaftStorage.newBuilder()
                         .withPrefix(String.format("partition-%s", partition.getId()))
-                        .withStorageLevel(StorageLevel.DISK)
-                        .withFlushOnCommit()
+                        .withStorageLevel(StorageLevel.MAPPED)
+                        .withFlushOnCommit(false)
                         .withSerializer(new AtomixSerializerAdapter(Serializer.using(StorageNamespaces.RAFT_STORAGE)))
                         .withDirectory(partition.getDataFolder())
                         .withMaxSegmentSize(MAX_SEGMENT_SIZE)