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https://issues.apache.org/jira/browse/HDFS-11311?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15825890#comment-15825890
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Yiqun Lin commented on HDFS-11311:
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HI [~afrimberger], thanks for reporting this. It's a interesting case that we
use {{fsck}} command. I make a test in my local, and follow the steps as that
mentioned in JIRA's description. But the test result seems a little different.
In my test, it runs ok and the {{Average replication factor}} will be smaller
than 3 (Maybe that's because my test data is too little).
{quote}
if (storageInfo.getBlockReportCount() == 0 && storageInfo.getState() !=
State.FAILED && storageInfo.numBlocks() > 0) {
{quote}
I'm +1 for this idea. It's a improvement for this. Finally attach my patch that
will reproduce this scenario. Now the test runs ok without change or with the
change that recommend above. I'd like to see other's further comment. :).
> 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
>
> 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 && storageInfo.numBlocks() > 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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