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Posted to hdfs-issues@hadoop.apache.org by "Wei-Chiu Chuang (JIRA)" <ji...@apache.org> on 2016/05/03 23:49:12 UTC
[jira] [Commented] (HDFS-10360) DataNode may format directory and
lose blocks if current/VERSION is missing
[ https://issues.apache.org/jira/browse/HDFS-10360?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15269669#comment-15269669 ]
Wei-Chiu Chuang commented on HDFS-10360:
----------------------------------------
In addition to the fix, it should also report the error via JMX.
> DataNode may format directory and lose blocks if current/VERSION is missing
> ---------------------------------------------------------------------------
>
> Key: HDFS-10360
> URL: https://issues.apache.org/jira/browse/HDFS-10360
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: datanode
> Reporter: Wei-Chiu Chuang
> Assignee: Wei-Chiu Chuang
> Attachments: HDFS-10360.001.patch
>
>
> Under certain circumstances, if the current/VERSION of a storage directory is missing, DataNode may format the storage directory even though _block files are not missing_.
> This is very easy to reproduce. Simply launch a HDFS cluster and create some files. Delete current/VERSION, and restart the data node.
> After the restart, the data node will format the directory and remove all existing block files:
> {noformat}
> 2016-05-03 12:57:15,387 INFO org.apache.hadoop.hdfs.server.common.Storage: Lock on /data/dfs/dn/in_use.lock acquired by nodename 5314@weichiu-dn-2.vpc.cloudera.com
> 2016-05-03 12:57:15,389 INFO org.apache.hadoop.hdfs.server.common.Storage: Storage directory /data/dfs/dn is not formatted for BP-787466439-172.26.24.43-1462305406642
> 2016-05-03 12:57:15,389 INFO org.apache.hadoop.hdfs.server.common.Storage: Formatting ...
> 2016-05-03 12:57:15,464 INFO org.apache.hadoop.hdfs.server.common.Storage: Analyzing storage directories for bpid BP-787466439-172.26.24.43-1462305406642
> 2016-05-03 12:57:15,464 INFO org.apache.hadoop.hdfs.server.common.Storage: Locking is disabled for /data/dfs/dn/current/BP-787466439-172.26.24.43-1462305406642
> 2016-05-03 12:57:15,465 INFO org.apache.hadoop.hdfs.server.common.Storage: Block pool storage directory /data/dfs/dn/current/BP-787466439-172.26.24.43-1462305406642 is not formatted for BP-787466439-172
> .26.24.43-1462305406642
> 2016-05-03 12:57:15,465 INFO org.apache.hadoop.hdfs.server.common.Storage: Formatting ...
> 2016-05-03 12:57:15,465 INFO org.apache.hadoop.hdfs.server.common.Storage: Formatting block pool BP-787466439-172.26.24.43-1462305406642 directory /data/dfs/dn/current/BP-787466439-172.26.24.43-1462305406642/current
> {noformat}
> The bug is: DataNode assumes that if none of {{current/VERSION}}, {{previous/}}, {{previous.tmp/}}, {{removed.tmp/}}, {{finalized.tmp/}} and {{lastcheckpoint.tmp/}} exists, the storage directory contains nothing important to HDFS and decides to format it.
> https://github.com/apache/hadoop/blob/trunk/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/common/Storage.java#L526-L545
> However, block files may still exist, and in my opinion, we should do everything possible to retain the block files.
> I have two suggestions:
> # check if {{current/}} directory is empty. If not, throw an InconsistentFSStateException in {{Storage#analyzeStorage}} instead of asumming its not formatted. Or,
> # In {{Storage#clearDirectory}}, before it formats the storage directory, rename or move {{current/}} directory. Also, log whatever is being renamed/moved.
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