Traditional Cluster Area Network(cLAN)’s evaluation model takes only latency, bandwidth, routing, congestion, network topology and some related aspects into consideration. Are these factors ENOUGH to describe the real applications’ communication behavior or predict its performance on cLAN? In the large quantity of NAS Parallel Benchmarks’ tests(version 2.4) on a modern supercomputer——DeepComp 1800, which is of LINUX Cluster architecture, it is found that the real performance of cLAN could be greatly affected by a special communication pattern(LU pattern). Further investigation reveals that the cLAN’s capacity of dealing with LU mode is independent of the known performance factors such as latency, bandwidth and so on. So it is necessary to take some new considerations on cLAN’s evaluation model and add one new factor to reflect the abnormal phenomenon. The new model also provides some challenges in parallel algorithm design and application performance improvement on the LINUX Cluster.