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From "Manoj Govindassamy (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-7877) Support maintenance state for datanodes
Date Fri, 10 Feb 2017 20:13:41 GMT

    [ https://issues.apache.org/jira/browse/HDFS-7877?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15861802#comment-15861802
] 

Manoj Govindassamy commented on HDFS-7877:
------------------------------------------

[~mingma],

[~dilaver] brought up a good point regarding the restrictions put for the range allowed for
the configuration {{dfs.namenode.maintenance.replication.min}}. Currently the allowed range
for Maintenance Min Replication 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.  So, any reasons why you
wanted to have Maintenance Min Replication range to be restrictive and less than or equal
to {{dfs.namenode.replication.min}} ? May be i am overlooking something here. Please clarify.


{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}

> Support maintenance state for datanodes
> ---------------------------------------
>
>                 Key: HDFS-7877
>                 URL: https://issues.apache.org/jira/browse/HDFS-7877
>             Project: Hadoop HDFS
>          Issue Type: New Feature
>          Components: datanode, namenode
>            Reporter: Ming Ma
>            Assignee: Ming Ma
>         Attachments: HDFS-7877-2.patch, HDFS-7877.patch, Supportmaintenancestatefordatanodes-2.pdf,
Supportmaintenancestatefordatanodes.pdf
>
>
> This requirement came up during the design for HDFS-7541. Given this feature is mostly
independent of upgrade domain feature, it is better to track it under a separate jira. The
design and draft patch will be available soon.



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