hdfs balancer doesn't balance blocks between datanodes
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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
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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