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From "Lei (Eddy) Xu (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HDFS-10360) DataNode may format directory and lose blocks if current/VERSION is missing
Date Tue, 17 May 2016 23:44:12 GMT

     [ https://issues.apache.org/jira/browse/HDFS-10360?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

Lei (Eddy) Xu updated HDFS-10360:
    Labels: dataloss datanode  (was: )

> 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
>              Labels: dataloss, datanode
>             Fix For: 2.9.0, 3.0.0-alpha1
>         Attachments: HDFS-10360.001.patch, HDFS-10360.002.patch, HDFS-10360.003.patch,
HDFS-10360.004.patch, HDFS-10360.004.patch, HDFS-10360.005.patch, HDFS-10360.007.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
> {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-
> 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-
> 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-
> 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- 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- directory /data/dfs/dn/current/BP-787466439-
> {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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