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https://issues.apache.org/jira/browse/HDFS-16182?focusedWorklogId=640933&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-640933
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ASF GitHub Bot logged work on HDFS-16182:
-----------------------------------------
Author: ASF GitHub Bot
Created on: 24/Aug/21 04:06
Start Date: 24/Aug/21 04:06
Worklog Time Spent: 10m
Work Description: Neilxzn edited a comment on pull request #3320:
URL: https://github.com/apache/hadoop/pull/3320#issuecomment-904304994
@jojochuang Agree with you. I think we should fix it.
In my cluster, we use BlockPlacementPolicyDefault to choose dn and the
number of SSD DN is much less than DISK DN. It may cause to some block that
should be placed to SSD DNs fallback to place DISK DNs when SSD DNs are too
busy or no enough place. Consider the following scenario.
1. Create empty file /foo_file
2. Set its storagepolicy to All_SSD
3. Put data to /foo_file
4. /foo_file gets 3 DISK dns for pipeline because SSD dns are too busy at
the beginning.
5. When it transfers data in pipeline, one of 3 DISK dns shut down.
6. The client need to get one new dn for existing pipeline in
DataStreamer$addDatanode2ExistingPipeline.
7. If SSD dns are available at the moment, namenode will choose the 3 SSD
dns and return it to the client. However, the client just need one new dn,
namenode returns 3 new SSD dn and the client threw exception in
DataStreamer$findNewDatanode.
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Issue Time Tracking
-------------------
Worklog Id: (was: 640933)
Time Spent: 50m (was: 40m)
> numOfReplicas is given the wrong value in
> BlockPlacementPolicyDefault$chooseTarget can cause DataStreamer to fail with
> Heterogeneous Storage
> -----------------------------------------------------------------------------------------------------------------------------------------------
>
> Key: HDFS-16182
> URL: https://issues.apache.org/jira/browse/HDFS-16182
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: namanode
> Affects Versions: 3.4.0
> Reporter: Max Xie
> Assignee: Max Xie
> Priority: Major
> Labels: pull-request-available
> Attachments: HDFS-16182.patch
>
> Time Spent: 50m
> Remaining Estimate: 0h
>
> In our hdfs cluster, we use heterogeneous storage to store data in SSD for a
> better performance. Sometimes hdfs client transfer data in pipline, it will
> throw IOException and exit. Exception logs are below:
> ```
> java.io.IOException: Failed to replace a bad datanode on the existing
> pipeline due to no more good datanodes being available to try. (Nodes:
> current=[DatanodeInfoWithStorage[dn01_ip:5004,DS-ef7882e0-427d-4c1e-b9ba-a929fac44fb4,DISK],
>
> DatanodeInfoWithStorage[dn02_ip:5004,DS-3871282a-ad45-4332-866a-f000f9361ecb,DISK],
>
> DatanodeInfoWithStorage[dn03_ip:5004,DS-a388c067-76a4-4014-a16c-ccc49c8da77b,SSD],
>
> DatanodeInfoWithStorage[dn04_ip:5004,DS-b81da262-0dd9-4567-a498-c516fab84fe0,SSD],
>
> DatanodeInfoWithStorage[dn05_ip:5004,DS-34e3af2e-da80-46ac-938c-6a3218a646b9,SSD]],
>
> original=[DatanodeInfoWithStorage[dn01_ip:5004,DS-ef7882e0-427d-4c1e-b9ba-a929fac44fb4,DISK],
>
> DatanodeInfoWithStorage[dn02_ip:5004,DS-3871282a-ad45-4332-866a-f000f9361ecb,DISK]]).
> The current failed datanode replacement policy is DEFAULT, and a client may
> configure this via
> 'dfs.client.block.write.replace-datanode-on-failure.policy' in its
> configuration.
> ```
> After search it, I found when existing pipline need replace new dn to
> transfer data, the client will get one additional dn from namenode and check
> that the number of dn is the original number + 1.
> ```
> ## DataStreamer$findNewDatanode
> if (nodes.length != original.length + 1) {
> throw new IOException(
> "Failed to replace a bad datanode on the existing pipeline "
> + "due to no more good datanodes being available to try. "
> + "(Nodes: current=" + Arrays.asList(nodes)
> + ", original=" + Arrays.asList(original) + "). "
> + "The current failed datanode replacement policy is "
> + dfsClient.dtpReplaceDatanodeOnFailure
> + ", and a client may configure this via '"
> + BlockWrite.ReplaceDatanodeOnFailure.POLICY_KEY
> + "' in its configuration.");
> }
> ```
> The root cause is that Namenode$getAdditionalDatanode returns multi datanodes
> , not one in DataStreamer.addDatanode2ExistingPipeline.
>
> Maybe we can fix it in BlockPlacementPolicyDefault$chooseTarget. I think
> numOfReplicas should not be assigned by requiredStorageTypes.
>
>
>
>
>
>
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