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https://issues.apache.org/jira/browse/HDFS-3070?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13243208#comment-13243208
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Aaron T. Myers commented on HDFS-3070:
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bq. I remember, in our Jenkins it will spawn separate JVM for each test class.
no?
True, but if that test class starts a MiniDFSCluster to run the balancer
against, then the test won't detect any problem with the balancer, since the
MiniDFSCluster will cause HdfsConfiguration to be class-loaded.
Uma, if I'm misunderstanding what you're proposing, perhaps you could post some
code to illustrate how this would work? If you do, I'll be sure to review it
promptly.
In the mean time, I'm going to go ahead and commit this patch since everyone
seems to agree that this will fix the bug.
> HDFS balancer doesn't ensure that hdfs-site.xml is loaded
> ---------------------------------------------------------
>
> Key: HDFS-3070
> URL: https://issues.apache.org/jira/browse/HDFS-3070
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: balancer
> Affects Versions: 2.0.0
> Reporter: Stephen Chu
> Assignee: Aaron T. Myers
> Attachments: HDFS-3070.patch, unbalanced_nodes.png,
> unbalanced_nodes_inservice.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
> active
> [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, threshold=1.0]
> Time Stamp Iteration# Bytes Already Moved Bytes Left To Move
> Bytes Being Moved
> 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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