Hello Amit, On Sun, Apr 24, 2011 at 5:00 AM, Amit Gupta <gupta.v.a...@gmail.com> wrote: > 1. I noticed there is a Source and Target, but there is also a ProxySource. > I havent been able to grasp the conceptual difference between a source and a > proxy source
The 'proxy' source is a DN that has a replica of a given block. This is used in order to even out the load across the DNs in the network. It would not be a good idea to put too much tx load onto the breaching DN, when you can copy off a replica. > 2. I'm also having trouble understanding the actual mechanics of a block > being relocated from > one datanode to the other. I understand that the communication with the > namenode occurs to change > metadata of the block being relocated accordingly, but have not understood > what does the actual copy > of the block itself. The block movement is done from a DN to another DN directly when it receives a command from the NameNode to do so (part of the heartbeat mechanism). -- Harsh J
