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http://issues.apache.org/jira/browse/HADOOP-692?page=comments#action_12449759 ]
Hairong Kuang commented on HADOOP-692:
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1. Network topology construction
Sould we consider a mobile network with laptops running datanode moving
around? Otherwise, once a datanode gets started, the possiblity of the node
moves to a different location is slim. I would simply update network toplogy
when a datanode registers or exits.
The # of hops between hubs can be specified in a configuration file which read
by the namenode at startup time.
2. Network toplogy interface
Doug, I like the interface that you described. But it looks like it can not
express the case when nodes are connected by a switch where the distance
between two nodes is 1. It also need to a method to expose all nodes that
belong to a hub.
2. block placement strategy
Allocating all blocks of a file to the same 3 racks limits the aggaregate read
bandwith. I do not see much of its benefit.
I am thinking to allow users to specify replica placement policy at runtime
when it sets the replication factor of a file. It can use any predefined
placement policy or set a user-defined placement policy.
Users may specify its replica placement policy using a declarative language.
Something like:
replica 1: same node
replica 2: same rack
replica 3: different rack
others: random
Any comment?
> 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.
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