final FSNamesystem namesystem = cluster.getNamesystem();
FileSystem fs = cluster.getFileSystem();
Path testPath = new Path("/tmp/TestRBWBlockInvalidation", "foo1");
out = fs.create(testPath, (short) 2);
out.writeBytes("HDFS-3157: " + testPath);
out.hsync();
cluster.startDataNodes(conf, 1, true, null, null, null);
String bpid = namesystem.getBlockPoolId();
ExtendedBlock blk = DFSTestUtil.getFirstBlock(fs, testPath);
Block block = blk.getLocalBlock();
DataNode dn = cluster.getDataNodes().get(0);