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https://issues.apache.org/jira/browse/HDFS-11311?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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André Frimberger updated HDFS-11311:
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Attachment: (was: HDFS-11311.001.patch)
> HDFS fsck continues to report all blocks present when DataNode is restarted
> with empty data directories
> -------------------------------------------------------------------------------------------------------
>
> Key: HDFS-11311
> URL: https://issues.apache.org/jira/browse/HDFS-11311
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: namenode
> Affects Versions: 2.7.3, 3.0.0-alpha1
> Reporter: André Frimberger
> Assignee: André Frimberger
> Attachments: HDFS-11311.001.patch,
> HDFS-11311-branch-3.0.0-alpha2.001.patch, HDFS-11311.reproduce.patch
>
>
> During cluster maintenance, we had to change parameters of the underlying
> disk filesystem and we stopped the DataNode, reformatted all of its data
> directories and started the DataNode again in under 10 minutes with no data
> and only the {{VERSION}} file present. Running fsck afterwards reports that
> all blocks are fully replicated, which does not reflect the true state of
> HDFS. If an administrator trusts {{fsck}} and continues to replace further
> DataNodes, *data will be lost!*
> Steps to reproduce:
> 1. Shutdown DataNode
> 2. Remove all BlockPools from all data directories (only {{VERSION}} file is
> present)
> 3. Startup DataNode in under 10.5 minutes
> 4. Run {{hdfs fsck /}}
> *Actual result:* Average replication is falsely shown as 3.0
> *Expected result:* Average replication factor is < 3.0
> *Workaround:* Trigger a block report with {{hdfs dfsadmin -triggerBlockReport
> $dn_host:$ipc_port}}
> *Cause:* The first block report is handled differently by NameNode and only
> added blocks are respected. This behaviour was introduced in HDFS-7980 for
> performance reasons. But is applied too widely and in our case data can be
> lost.
> *Fix:* We suggest using stricter conditions on applying
> {{processFirstBlockReport}} in {{BlockManager:processReport()}}:
> Change
> {code}
> if (storageInfo.getBlockReportCount() == 0) {
> // The first block report can be processed a lot more efficiently than
> // ordinary block reports. This shortens restart times.
> processFirstBlockReport(storageInfo, newReport);
> } else {
> invalidatedBlocks = processReport(storageInfo, newReport);
> }
> {code}
> to
> {code}
> if (storageInfo.getBlockReportCount() == 0 && storageInfo.getState() !=
> State.FAILED && newReport.getNumberOfBlocks() > 0) {
> // The first block report can be processed a lot more efficiently than
> // ordinary block reports. This shortens restart times.
> processFirstBlockReport(storageInfo, newReport);
> } else {
> invalidatedBlocks = processReport(storageInfo, newReport);
> }
> {code}
> In case the DataNode reports no blocks for a data directory, it might be a
> new DataNode or the data directory may have been emptied for whatever reason
> (offline replacement of storage, reformatting of data disk, etc.). In either
> case, the changes should be reflected in the output of {{fsck}} in less than
> 6 hours to prevent data loss due to misleading output.
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