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https://issues.apache.org/jira/browse/HDFS-7842?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14336444#comment-14336444
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Brahma Reddy Battula commented on HDFS-7842:
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AFAIK {{-rollingUpgrade downgrade}} no longer availble,, Please check
following link for same..
https://issues.apache.org/jira/browse/HDFS-7302?focusedCommentId=14335036&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-14335036
{quote}
Restoring blocks from trash after downgrade can be avoided.
{quote}
I feel,HDFS-7645 will solve this..
> Blocks missed while performing downgrade immediately after rolling back the
> cluster.
> ------------------------------------------------------------------------------------
>
> Key: HDFS-7842
> URL: https://issues.apache.org/jira/browse/HDFS-7842
> Project: Hadoop HDFS
> Issue Type: Bug
> Reporter: J.Andreina
> Assignee: J.Andreina
> Priority: Critical
>
> Performing downgrade immediately after rolling back the cluster , will
> replace the blocks from trash
> Since the block id for the files created before rollback will be same as the
> file created before downgrade, namenode will get into safemode , as the block
> size reported from Datanode will be different from the one in block map
> (corrupted blocks) .
> Steps to Reproduce
> {noformat}
> Step 1: Prepare rolling upgrade using "hdfs dfsadmin -rollingUpgrade prepare"
> Step 2: Shutdown SNN and NN
> Step 3: Start NN with the "hdfs namenode -rollingUpgrade started" option.
> Step 4: Executed "hdfs dfsadmin -shutdownDatanode <DATANODE_HOST:IPC_PORT>
> upgrade" and restarted Datanode
> Step 5: Create File_1 of size 11526
> Step 6: Shutdown both NN and DN
> Step 7: Start NNs with the "hdfs namenode -rollingUpgrade rollback" option.
> Start DNs with the "-rollback" option.
> Step 8: Prepare rolling upgrade using "hdfs dfsadmin -rollingUpgrade prepare"
> Step 9: Shutdown SNN and NN
> Step 10: Start NN with the "hdfs namenode -rollingUpgrade started" option .
> Step 11: Executed "hdfs dfsadmin -shutdownDatanode <DATANODE_HOST:IPC_PORT>
> upgrade" and restarted Datanode
> step 12: Add file File_2 with size 6324 (which has same blockid as previous
> created File_1 with block size 11526)
> Step 13: Shutdown both NN and DN
> Step 14: Start NNs with the "hdfs namenode -rollingUpgrade downgrade"
> option.Start DNs normally.
> {noformat}
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