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https://issues.apache.org/jira/browse/HDFS-11412?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15868977#comment-15868977
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Ming Ma commented on HDFS-11412:
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Thanks [~manojg].
* Regarding whether to use default replication factor or max replication
factor, do you care about the following use case? default == 3, max = 30. Block
A have large replication factor 30 and would like to keep at least 20 live
replicas around during maintenance. Then put 20 nodes with replicas of Block A
into maintenance at the same time. To make sure at least 20 live replicas after
maintenance, the system need to honor minReplicationToBeInMaintenance == 20.
* Impact on {{getExpectedLiveRedundancyNum}} calculation. Set
minReplicationToBeInMaintenance to 3. Block B's replication factor is 2. Put
one of its replicas into maintenance. Inside function
{{getExpectedLiveRedundancyNum}}, {{Math.max(expectedRedundancy -
numberReplicas.maintenanceReplicas(), getMinReplicationToBeInMaintenance())}}
== 3. Ideally the function should return 2.
> Maintenance minimum replication config value allowable range should be {0 -
> DefaultReplication}
> -----------------------------------------------------------------------------------------------
>
> Key: HDFS-11412
> URL: https://issues.apache.org/jira/browse/HDFS-11412
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: datanode, namenode
> Affects Versions: 3.0.0-alpha1
> Reporter: Manoj Govindassamy
> Assignee: Manoj Govindassamy
> Attachments: HDFS-11412.01.patch
>
>
> Currently the allowed value range for Maintenance Min Replication
> {{dfs.namenode.maintenance.replication.min}} is 0 to
> {{dfs.namenode.replication.min}} (default=1). Users wanting not to affect the
> performance of the cluster would wish to have the Maintenance Min Replication
> number greater than 1, say 2. In the current design, it is possible to have
> this Maintenance Min Replication configuration, but only after changing the
> NameNode level Block Min Replication to 2, and which could slowdown the
> overall latency for client writes.
> Technically speaking we should be allowing Maintenance Min Replication to be
> in range 0 to dfs.replication.max.
> * There is always config value of 0 for users not wanting any
> availability/performance during maintenance.
> * And, performance centric workloads can still get maintenance done without
> major disruptions by having a bigger Maintenance Min Replication. Setting the
> upper limit as dfs.replication.max could be an overkill as it could trigger
> re-replication which Maintenance State is trying to avoid. So, we could allow
> the {{dfs.namenode.maintenance.replication.min}} in the range {{0 to
> dfs.replication}}
> {noformat}
> if (minMaintenanceR < 0) {
> throw new IOException("Unexpected configuration parameters: "
> + DFSConfigKeys.DFS_NAMENODE_MAINTENANCE_REPLICATION_MIN_KEY
> + " = " + minMaintenanceR + " < 0");
> }
> if (minMaintenanceR > minR) {
> throw new IOException("Unexpected configuration parameters: "
> + DFSConfigKeys.DFS_NAMENODE_MAINTENANCE_REPLICATION_MIN_KEY
> + " = " + minMaintenanceR + " > "
> + DFSConfigKeys.DFS_NAMENODE_REPLICATION_MIN_KEY
> + " = " + minR);
> {noformat}
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