[HDFS-16182] numOfReplicas is given the wrong value in BlockPlacementPolicyDefault$chooseTarget can cause DataStreamer to fail with Heterogeneous Storage

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 3.4.0
• Fix Version/s: 3.4.0, 3.3.2, 3.2.4
• Component/s: namanode
• Labels: pull-request-available
• Assignee: Max Xie
• Reporter: Max Xie
• Created: 23/Aug/21 07:25
• Updated: 12/Jul/22 10:52
• Resolved: 16/Nov/21 15:09

Description

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.

 

   

 

 

 

 

Issue Links

• links to: GitHub Pull Request #3320