the performance of HDFS

[Da Zheng]

Hello,

I try to measure the performance of HDFS, but the writing rate is quite 
low. When the replication factor is 1, the rate of writing to HDFS is 
about 60MB/s. When the replication factor is 3, the rate drops 
significantly to about 15MB/s. Even though the actual rate of writing 
data to the disk is about 45MB/s, it's still much lower than when 
replication factor is 1. The link between two nodes in the cluster is 
1Gbps. CPU is Dual-Core AMD Opteron(tm) Processor 2212, so CPU isn't 
bottleneck either. I thought I should be able to saturate the disk very 
easily. I wonder where the bottleneck is. What is the throughput for 
writing on a Hadoop cluster when the replication factor is 3?

Thanks,
Da