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From "Stephen Chu (Created) (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HDFS-3070) hdfs balancer doesn't balance blocks between datanodes
Date Fri, 09 Mar 2012 00:55:57 GMT
hdfs balancer doesn't balance blocks between datanodes

                 Key: HDFS-3070
                 URL: https://issues.apache.org/jira/browse/HDFS-3070
             Project: Hadoop HDFS
          Issue Type: Bug
          Components: balancer
    Affects Versions: 0.24.0
            Reporter: Stephen Chu
         Attachments: unbalanced_nodes.png

I TeraGenerated data into DataNodes styx01 and styx02. Looking at the web UI, both have over
3% disk usage.
Attached is a screenshot of the Live Nodes web UI.

On styx01, I run the _hdfs balancer_ command with threshold 1% and don't see the blocks being
balanced across all 4 datanodes (all blocks on styx01 and styx02 stay put).

HA is currently enabled.

[schu@styx01 ~]$ hdfs haadmin -getServiceState nn1
[schu@styx01 ~]$ hdfs balancer -threshold 1
12/03/08 10:10:32 INFO balancer.Balancer: Using a threshold of 1.0
12/03/08 10:10:32 INFO balancer.Balancer: namenodes = []
12/03/08 10:10:32 INFO balancer.Balancer: p         = Balancer.Parameters[BalancingPolicy.Node,
Time Stamp               Iteration#  Bytes Already Moved  Bytes Left To Move  Bytes Being
Balancing took 95.0 milliseconds
[schu@styx01 ~]$ 

I believe with a threshold of 1% the balancer should trigger blocks being moved across DataNodes,
right? I am curious about the "namenode = []" from the above output.

[schu@styx01 ~]$ hadoop version
Hadoop 0.24.0-SNAPSHOT
Subversion git://styx01.sf.cloudera.com/home/schu/hadoop-common/hadoop-common-project/hadoop-common
-r f6a577d697bbcd04ffbc568167c97b79479ff319
Compiled by schu on Thu Mar  8 15:32:50 PST 2012
>From source with checksum ec971a6e7316f7fbf471b617905856b8

>From http://hadoop.apache.org/hdfs/docs/r0.21.0/api/org/apache/hadoop/hdfs/server/balancer/Balancer.html:
The threshold parameter is a fraction in the range of (0%, 100%) with a default value of 10%.
The threshold sets a target for whether the cluster is balanced. A cluster is balanced if
for each datanode, the utilization of the node (ratio of used space at the node to total capacity
of the node) differs from the utilization of the (ratio of used space in the cluster to total
capacity of the cluster) by no more than the threshold value. The smaller the threshold, the
more balanced a cluster will become. It takes more time to run the balancer for small threshold
values. Also for a very small threshold the cluster may not be able to reach the balanced
state when applications write and delete files concurrently.

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