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https://issues.apache.org/jira/browse/HDFS-4229?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13504205#comment-13504205
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Brock Noland commented on HDFS-4229:
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>From a user perspective, I am not expecting a negative number and as such, a
>simple solution such as Math.max(used, 0) would be acceptable.
> HDFS can report negative DFS Used on clusters with very small amounts of data
> -----------------------------------------------------------------------------
>
> Key: HDFS-4229
> URL: https://issues.apache.org/jira/browse/HDFS-4229
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: name-node
> Affects Versions: 2.0.2-alpha
> Reporter: Brock Noland
> Priority: Minor
>
> I had a near empty HDFS instance where I was creating a file and deleting it
> very quickly. I noticed that HDFS sometimes reported a negative DFS used.
> {noformat}
> root@brock0-1 ~]# sudo -u hdfs -i hdfs dfsadmin -report
> Configured Capacity: 97233235968 (90.56 GB)
> Present Capacity: 84289609707 (78.5 GB)
> DFS Remaining: 84426645504 (78.63 GB)
> DFS Used: -137035797 (-133824.02 KB)
> DFS Used%: -0.16%
> Under replicated blocks: 0
> Blocks with corrupt replicas: 0
> Missing blocks: 0
> -------------------------------------------------
> Datanodes available: 1 (1 total, 0 dead)
> Live datanodes:
> Name: 127.0.0.1:50010 (localhost)
> Hostname: brock0-1.ent.cloudera.com
> Decommission Status : Normal
> Configured Capacity: 97233235968 (90.56 GB)
> DFS Used: -137035797 (-133824.02 KB)
> Non DFS Used: 12943626261 (12.05 GB)
> DFS Remaining: 84426645504 (78.63 GB)
> DFS Used%: -0.14%
> DFS Remaining%: 86.83%
> Last contact: Thu Nov 22 18:25:37 PST 2012
> [root@brock0-1 ~]# sudo -u hdfs -i hdfs dfsadmin -report
> Configured Capacity: 97233235968 (90.56 GB)
> Present Capacity: 84426973184 (78.63 GB)
> DFS Remaining: 84426629120 (78.63 GB)
> DFS Used: 344064 (336 KB)
> DFS Used%: 0%
> Under replicated blocks: 0
> Blocks with corrupt replicas: 0
> Missing blocks: 0
> -------------------------------------------------
> Datanodes available: 1 (1 total, 0 dead)
> Live datanodes:
> Name: 127.0.0.1:50010 (localhost)
> Hostname: brock0-1.ent.cloudera.com
> Decommission Status : Normal
> Configured Capacity: 97233235968 (90.56 GB)
> DFS Used: 344064 (336 KB)
> Non DFS Used: 12806262784 (11.93 GB)
> DFS Remaining: 84426629120 (78.63 GB)
> DFS Used%: 0%
> DFS Remaining%: 86.83%
> Last contact: Thu Nov 22 18:28:47 PST 2012
> {noformat}
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