[HDFS-795] DFS Write pipeline does not detect defective datanode correctly in some cases (HADOOP-3339)

• Type: Bug
• Status: Resolved
• Priority: Critical
• Resolution: Duplicate
• Affects Version/s: 0.20.1
• Fix Version/s: 0.20.2
• Component/s: hdfs-client
• Assignee: Unassigned
• Reporter: Raghu Angadi
• Created: 08/May/09 19:11
• Updated: 18/Dec/09 01:58
• Resolved: 18/Dec/09 01:58

Description

HDFS write pipeline does not select the correct datanode in some error cases. One example : say DN2 is the second datanode and write to it times out since it is in a bad state.. pipeline actually removes the first datanode. If such a datanode happens to be the last one in the pipeline, write is aborted completely with a hard error.

Essentially the error occurs when writing to a downstream datanode fails rather than reading. This bug was actually fixed in 0.18 (HADOOP-3339). But HADOOP-1700 essentially reverted it. I am not sure why.

It is absolutely essential for HDFS to handle failures on subset of datanodes in a pipeline. We should not have at least known bugs that lead to hard failures.

I will attach patch for a hack that illustrates this problem. Still thinking of how an automated test would look like for this one.

My preferred target for this fix is 0.20.1.

Issue Links

• duplicates: HDFS-101 DFS write pipeline : DFSClient sometimes does not detect second datanode failure