[ http://issues.apache.org/jira/browse/HADOOP-692?page=comments#action_12448818 ] Koji Noguchi commented on HADOOP-692: -------------------------------------
If the nodes are connected with switches, I think it'll be hard to figure out how many 'hops' there are between nodes. Switches are transparent to the nodes. For example, traceroute only shows the routers and not the switches. > Rack-aware Replica Placement > ---------------------------- > > Key: HADOOP-692 > URL: http://issues.apache.org/jira/browse/HADOOP-692 > Project: Hadoop > Issue Type: Improvement > Components: dfs > Affects Versions: 0.8.0 > Reporter: Hairong Kuang > Assigned To: Hairong Kuang > Fix For: 0.9.0 > > > This issue assumes that HDFS runs on a cluster of computers that spread > across many racks. Communication between two nodes on different racks needs > to go through switches. Bandwidth in/out of a rack may be less than the total > bandwidth of machines in the rack. The purpose of rack-aware replica > placement is to improve data reliability, availability, and network bandwidth > utilization. The basic idea is that each data node determines to which rack > it belongs at the startup time and notifies the name node of the rack id upon > registration. The name node maintains a rackid-to-datanode map and tries to > place replicas across racks. -- This message is automatically generated by JIRA. - If you think it was sent incorrectly contact one of the administrators: http://issues.apache.org/jira/secure/Administrators.jspa - For more information on JIRA, see: http://www.atlassian.com/software/jira
