Max Xie created HDFS-16182:
-------------------------------
Summary: numOfReplicas is given the wrong value in
BlockPlacementPolicyDefault$chooseTarget can cause DataStreamer to fail with
Heterogeneous Storage
Key: HDFS-16182
URL: https://issues.apache.org/jira/browse/HDFS-16182
Project: Hadoop HDFS
Issue Type: Bug
Components: namanode
Affects Versions: 3.4.0
Reporter: Max Xie
In our hdfs cluster, we use heterogeneous storage to store data in SSD for a
better performance. Sometimes hdfs client transfer data in pipline, it will
throw IOException and exit. Exception logs are below:
```
java.io.IOException: Failed to replace a bad datanode on the existing pipeline
due to no more good datanodes being available to try. (Nodes:
current=[DatanodeInfoWithStorage[dn01_ip:5004,DS-ef7882e0-427d-4c1e-b9ba-a929fac44fb4,DISK],
DatanodeInfoWithStorage[dn02_ip:5004,DS-3871282a-ad45-4332-866a-f000f9361ecb,DISK],
DatanodeInfoWithStorage[dn03_ip:5004,DS-a388c067-76a4-4014-a16c-ccc49c8da77b,SSD],
DatanodeInfoWithStorage[dn04_ip:5004,DS-b81da262-0dd9-4567-a498-c516fab84fe0,SSD],
DatanodeInfoWithStorage[dn05_ip:5004,DS-34e3af2e-da80-46ac-938c-6a3218a646b9,SSD]],
original=[DatanodeInfoWithStorage[dn01_ip:5004,DS-ef7882e0-427d-4c1e-b9ba-a929fac44fb4,DISK],
DatanodeInfoWithStorage[dn02_ip:5004,DS-3871282a-ad45-4332-866a-f000f9361ecb,DISK]]).
The current failed datanode replacement policy is DEFAULT, and a client may
configure this via 'dfs.client.block.write.replace-datanode-on-failure.policy'
in its configuration.
```
After search it, I found when existing pipline need replace new dn to
transfer data, the client will get one additional dn from namenode and check
that the number of dn is the original number + 1.
```
## DataStreamer$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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