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https://issues.apache.org/jira/browse/HDFS-17299?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17799702#comment-17799702
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Ayush Saxena edited comment on HDFS-17299 at 12/22/23 1:53 PM:
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{quote}So it will take 1230000 ms (20.5mins) to detect that datanode is dead.
{quote}
Did you explore
{{dfs.namenode.avoid.write.stale.datanode}} and
{{{}dfs.namenode.stale.datanode.interval{}}}. I believe that can bring down
your value to few seconds, 30 by default but you can get that down to
3*Heartbeat interval IIRC.
You should find the reason why the nodes were chosen in 1 AZ only, why no node
was chosen in other 2 AZ, it will fallback to choosing nodes in 1 AZ(rack) only
when it fails to spread them to different racks
was (Author: ayushtkn):
{quote}So it will take 1230000 ms (20.5mins) to detect that datanode is dead.
{quote}
Did you explore
dfs.namenode.avoid.write.stale.datanode and
{{{}dfs.namenode.stale.datanode.interval{}}}. I believe that can bring down
your value to few seconds, 30 by default but you can get that down to
3*Heartbeat interval IIRC.
You should find the reason why the nodes were chosen in 1 AZ only, why no node
was chosen in other 2 AZ, it will fallback to choosing nodes in 1 AZ(rack) only
when it fails to spread them to different racks
> HDFS is not rack failure tolerant while creating a new file.
> ------------------------------------------------------------
>
> Key: HDFS-17299
> URL: https://issues.apache.org/jira/browse/HDFS-17299
> Project: Hadoop HDFS
> Issue Type: Bug
> Affects Versions: 2.10.1
> Reporter: Rushabh Shah
> Priority: Critical
>
> Recently we saw an HBase cluster outage when we mistakenly brought down 1 AZ.
> Our configuration:
> 1. We use 3 Availability Zones (AZs) for fault tolerance.
> 2. We use BlockPlacementPolicyRackFaultTolerant as the block placement policy.
> 3. We use the following configuration parameters:
> dfs.namenode.heartbeat.recheck-interval: 600000
> dfs.heartbeat.interval: 3
> So it will take 1230000 ms (20.5mins) to detect that datanode is dead.
>
> Steps to reproduce:
> # Bring down 1 AZ.
> # HBase (HDFS client) tries to create a file (WAL file) and then calls
> hflush on the newly created file.
> # DataStreamer is not able to find blocks locations that satisfies the rack
> placement policy (one copy in each rack which essentially means one copy in
> each AZ)
> # Since all the datanodes in that AZ are down but still alive to namenode,
> the client gets different datanodes but still all of them are in the same AZ.
> See logs below.
> # HBase is not able to create a WAL file and it aborts the region server.
>
> Relevant logs from hdfs client and namenode
>
> {noformat}
> 2023-12-16 17:17:43,818 INFO [on default port 9000] FSNamesystem.audit -
> allowed=true ugi=hbase/<rs-name> (auth:KERBEROS) ip=<rs-IP>
> cmd=create src=/hbase/WALs/<WAL-file> dst=null
> 2023-12-16 17:17:43,978 INFO [on default port 9000] hdfs.StateChange -
> BLOCK* allocate blk_1214652565_140946716, replicas=<AZ-1-dn-1>:50010,
> <AZ-2-dn-1>:50010, <AZ-3-dn-1>:50010 for /hbase/WALs/<WAL-file>
> 2023-12-16 17:17:44,061 INFO [Thread-39087] hdfs.DataStreamer - Exception in
> createBlockOutputStream
> java.io.IOException: Got error, status=ERROR, status message , ack with
> firstBadLink as <AZ-2-dn-1>:50010
> at
> org.apache.hadoop.hdfs.protocol.datatransfer.DataTransferProtoUtil.checkBlockOpStatus(DataTransferProtoUtil.java:113)
> at
> org.apache.hadoop.hdfs.DataStreamer.createBlockOutputStream(DataStreamer.java:1747)
> at
> org.apache.hadoop.hdfs.DataStreamer.nextBlockOutputStream(DataStreamer.java:1651)
> at org.apache.hadoop.hdfs.DataStreamer.run(DataStreamer.java:715)
> 2023-12-16 17:17:44,061 WARN [Thread-39087] hdfs.DataStreamer - Abandoning
> BP-179318874-<NN-IP>-1594838129323:blk_1214652565_140946716
> 2023-12-16 17:17:44,179 WARN [Thread-39087] hdfs.DataStreamer - Excluding
> datanode
> DatanodeInfoWithStorage[<AZ-2-dn-1>:50010,DS-a493abdb-3ac3-49b1-9bfb-848baf5c1c2c,DISK]
> 2023-12-16 17:17:44,339 INFO [on default port 9000] hdfs.StateChange -
> BLOCK* allocate blk_1214652580_140946764, replicas=<AZ-1-dn-2>:50010,
> <AZ-3-dn-2>:50010, <AZ-2-dn-2>:50010 for /hbase/WALs/<WAL-file>
> 2023-12-16 17:17:44,369 INFO [Thread-39087] hdfs.DataStreamer - Exception in
> createBlockOutputStream
> java.io.IOException: Got error, status=ERROR, status message , ack with
> firstBadLink as <AZ-2-dn-2>:50010
> at
> org.apache.hadoop.hdfs.protocol.datatransfer.DataTransferProtoUtil.checkBlockOpStatus(DataTransferProtoUtil.java:113)
> at
> org.apache.hadoop.hdfs.DataStreamer.createBlockOutputStream(DataStreamer.java:1747)
> at
> org.apache.hadoop.hdfs.DataStreamer.nextBlockOutputStream(DataStreamer.java:1651)
> at org.apache.hadoop.hdfs.DataStreamer.run(DataStreamer.java:715)
> 2023-12-16 17:17:44,369 WARN [Thread-39087] hdfs.DataStreamer - Abandoning
> BP-179318874-NN-IP-1594838129323:blk_1214652580_140946764
> 2023-12-16 17:17:44,454 WARN [Thread-39087] hdfs.DataStreamer - Excluding
> datanode
> DatanodeInfoWithStorage[AZ-2-dn-2:50010,DS-46bb45cc-af89-46f3-9f9d-24e4fdc35b6d,DISK]
> 2023-12-16 17:17:44,522 INFO [on default port 9000] hdfs.StateChange -
> BLOCK* allocate blk_1214652594_140946796, replicas=<AZ-1-dn-2>:50010,
> <AZ-2-dn-3>:50010, <AZ-3-dn-3>:50010 for /hbase/WALs/<WAL-file>
> 2023-12-16 17:17:44,712 INFO [Thread-39087] hdfs.DataStreamer - Exception in
> createBlockOutputStream
> java.io.IOException: Got error, status=ERROR, status message , ack with
> firstBadLink as <AZ-2-dn-3>:50010
> at
> org.apache.hadoop.hdfs.protocol.datatransfer.DataTransferProtoUtil.checkBlockOpStatus(DataTransferProtoUtil.java:113)
> at
> org.apache.hadoop.hdfs.DataStreamer.createBlockOutputStream(DataStreamer.java:1747)
> at
> org.apache.hadoop.hdfs.DataStreamer.nextBlockOutputStream(DataStreamer.java:1651)
> at org.apache.hadoop.hdfs.DataStreamer.run(DataStreamer.java:715)
> 2023-12-16 17:17:44,712 WARN [Thread-39087] hdfs.DataStreamer - Abandoning
> BP-179318874-NN-IP-1594838129323:blk_1214652594_140946796
> 2023-12-16 17:17:44,732 WARN [Thread-39087] hdfs.DataStreamer - Excluding
> datanode
> DatanodeInfoWithStorage[<AZ-2-dn-3>:50010,DS-86b77463-a26f-4f42-ae1b-21b75c407203,DISK]
> 2023-12-16 17:17:44,855 INFO [on default port 9000] hdfs.StateChange -
> BLOCK* allocate blk_1214652607_140946850, replicas=<AZ-1-dn-4>:50010,
> <AZ-2-dn-4>:50010, <AZ-3-dn-4>:50010 for /hbase/WALs/<WAL-file>
> 2023-12-16 17:17:44,867 INFO [Thread-39087] hdfs.DataStreamer - Exception in
> createBlockOutputStream
> java.io.IOException: Got error, status=ERROR, status message , ack with
> firstBadLink as <AZ-2-dn-4>:50010
> at
> org.apache.hadoop.hdfs.protocol.datatransfer.DataTransferProtoUtil.checkBlockOpStatus(DataTransferProtoUtil.java:113)
> at
> org.apache.hadoop.hdfs.DataStreamer.createBlockOutputStream(DataStreamer.java:1747)
> at
> org.apache.hadoop.hdfs.DataStreamer.nextBlockOutputStream(DataStreamer.java:1651)
> at org.apache.hadoop.hdfs.DataStreamer.run(DataStreamer.java:715)
> 2023-12-16 17:17:44,988 WARN [Thread-39087] hdfs.DataStreamer - DataStreamer
> Exception
> java.io.IOException: Unable to create new block.
> at
> org.apache.hadoop.hdfs.DataStreamer.nextBlockOutputStream(DataStreamer.java:1665)
> at org.apache.hadoop.hdfs.DataStreamer.run(DataStreamer.java:715)
> 2023-12-16 17:17:44,988 WARN [Thread-39087] hdfs.DataStreamer - Could not
> get block locations. Source file "/hbase/WALs/<WAL-file>" - Aborting...
> {noformat}
>
> *Proposed fix:*
> Client always correctly identifies the bad datanode in the pipeline.
> The number of retries dfs client makes is controlled by
> dfs.client.block.write.retries (defaults to 3). So in total it tries 4 times
> to create the pipeline.
> So on the 3rd or 4th attempt, if we see all the excluded nodes in the
> pipeline belongs to the same rack, we can pass the hint to namenode to
> exclude that rack for the next block.
> Once that rack is back online, Replication monitor will handle to replicate
> that block to that rack.
>
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