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From: Brahma Reddy Battula <brahmareddy.battula@huawei.com>
To: "hdfs-dev@hadoop.apache.org" <hdfs-dev@hadoop.apache.org>
Subject: Issue in handling checksum errors in write pipeline
Thread-Topic: Issue in handling checksum errors in write pipeline
Thread-Index: AdHqUcgFCr3dc0J8RcmSn/FJ5eWfjg==
Date: Sat, 30 Jul 2016 11:03:59 +0000
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archived-at: Sat, 30 Jul 2016 11:04:29 -0000

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Hello


We had come across one issue, where write is failed even 7 DN's are availab=
le due to network fault at one datanode which is LAST_IN_PIPELINE. It will =
be similar to HDFS-6937 .

Scenario : (DN3 has N/W Fault and Min repl=3D2).

Write pipeline:
DN1->DN2->DN3  =3D> DN3 Gives ERROR_CHECKSUM ack. And so DN2 marked as bad
DN1->DN4-> DN3 =3D> DN3 Gives ERROR_CHECKSUM ack. And so DN4 is marked as b=
ad
....
And so on ( all the times DN3 is LAST_IN_PIPELINE) ... Continued till no mo=
re datanodes to construct the pipeline.

Thinking we can handle like below:

Instead of throwing IOException for ERROR_CHECKSUM ack from downstream, If =
we can send back the pipeline ack and client side we can replace both DN2 a=
nd DN3 with new nodes as we can't decide on which is having network problem=
.


Please give you views the possible fix..


--Brahma Reddy Battula


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