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https://issues.apache.org/jira/browse/HDFS-11030?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15623509#comment-15623509
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Jitendra Nath Pandey commented on HDFS-11030:
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+1. Thanks for the patch [~liuml07]
> TestDataNodeVolumeFailure#testVolumeFailure is flaky (though passing)
> ---------------------------------------------------------------------
>
> Key: HDFS-11030
> URL: https://issues.apache.org/jira/browse/HDFS-11030
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: datanode, test
> Affects Versions: 2.7.0
> Reporter: Mingliang Liu
> Assignee: Mingliang Liu
> Attachments: HDFS-11030-branch-2.000.patch, HDFS-11030.000.patch
>
>
> TestDataNodeVolumeFailure#testVolumeFailure fails a volume and verifies the
> blocks and files are replicated correctly.
> # To fail a volume, it deletes all the blocks and sets the data dir read only.
> {code:title=testVolumeFailure() snippet}
> // fail the volume
> // delete/make non-writable one of the directories (failed volume)
> data_fail = new File(dataDir, "data3");
> failedDir = MiniDFSCluster.getFinalizedDir(dataDir,
> cluster.getNamesystem().getBlockPoolId());
> if (failedDir.exists() &&
> //!FileUtil.fullyDelete(failedDir)
> !deteteBlocks(failedDir)
> ) {
> throw new IOException("Could not delete hdfs directory '" + failedDir +
> "'");
> }
> data_fail.setReadOnly();
> failedDir.setReadOnly();
> {code}
> However, there are two bugs here, which make the blocks not deleted.
> #- The {{failedDir}} directory for finalized blocks is not calculated
> correctly. It should use {{data_fail}} instead of {{dataDir}} as the base
> directory.
> #- When deleting block files in {{deteteBlocks(failedDir)}}, it assumes that
> there is no subdirectories in the data dir. This assumption was also noted in
> the comments.
> {quote}
> // we use only small number of blocks to avoid creating subdirs in the
> data dir..
> {quote}
> This is not true. On my local cluster and MiniDFSCluster, there will be
> subdir0/subdir0/ two level directories regardless of the number of blocks.
> # Meanwhile, to fail a volume, it also needs to trigger the DataNode removing
> the volume and send block report to NN. This is basically in the
> {{triggerFailure()}} method.
> {code}
> private void triggerFailure(String path, long size) throws IOException {
> NamenodeProtocols nn = cluster.getNameNodeRpc();
> List<LocatedBlock> locatedBlocks =
> nn.getBlockLocations(path, 0, size).getLocatedBlocks();
>
> for (LocatedBlock lb : locatedBlocks) {
> DatanodeInfo dinfo = lb.getLocations()[1];
> ExtendedBlock b = lb.getBlock();
> try {
> accessBlock(dinfo, lb);
> } catch (IOException e) {
> System.out.println("Failure triggered, on block: " + b.getBlockId() +
>
> "; corresponding volume should be removed by now");
> break;
> }
> }
> }
> {code}
> Accessing those blocks will not trigger failures if the directory is
> read-only (while the block files are all there). I ran the tests multiple
> times without triggering this failure. We have to write new block files to
> the data directories, or we should have deleted the blocks correctly. I think
> we need to add some assertion code after triggering the volume failure. The
> assertions should check the datanode volume failure summary explicitly to
> make sure a volume failure is triggered (and noticed).
> # To make sure the NameNode be aware of the volume failure, the code
> explictily send block reports to NN.
> {code:title=TestDataNodeVolumeFailure#testVolumeFailure()}
> cluster.getNameNodeRpc().blockReport(dnR, bpid, reports,
> new BlockReportContext(1, 0, System.nanoTime(), 0, false));
> {code}
> Generating block report code is complex, which is actually the internal logic
> of {{BPServiceActor}}. We may have to update this code it changes. In fact,
> the volume failure is now sent by DataNode via heartbeats. We should trigger
> a heartbeat request here; and make sure the NameNode handles the heartbeat
> before we verify the block states.
> # When verifying via {{verify()}}, it counts the real block files and assert
> that real block files plus underreplicated blocks should cover all blocks.
> Before counting underreplicated blocks, it triggered the {{BlockManager}} to
> compute the datanode work:
> {code}
> // force update of all the metric counts by calling computeDatanodeWork
> BlockManagerTestUtil.getComputedDatanodeWork(fsn.getBlockManager());
> {code}
> However, counting physical block files and underreplicated blocks are not
> atomic. The NameNode will inform of the DataNode the computed work at next
> heartbeat. So I think this part of code may fail when some blocks are
> replicated and the number of physical block files is made stale. To avoid
> this case, I think we should keep the DataNode from sending the heartbeat
> after that. A simple solution is to set {{dfs.heartbeat.interval}} long
> enough.
> This unit test has been there for years and it seldom fails, just because
> it's never triggered a real volume failure.
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