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From "ASF GitHub Bot (Jira)" <j...@apache.org>
Subject [jira] [Work logged] (HDDS-1881) Design doc: decommissioning in Ozone
Date Wed, 28 Aug 2019 17:15:01 GMT

     [ https://issues.apache.org/jira/browse/HDDS-1881?focusedWorklogId=303053&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-303053
]

ASF GitHub Bot logged work on HDDS-1881:
----------------------------------------

                Author: ASF GitHub Bot
            Created on: 28/Aug/19 17:14
            Start Date: 28/Aug/19 17:14
    Worklog Time Spent: 10m 
      Work Description: anuengineer commented on pull request #1196: HDDS-1881. Design doc:
decommissioning in Ozone
URL: https://github.com/apache/hadoop/pull/1196#discussion_r309752274
 
 

 ##########
 File path: hadoop-hdds/docs/content/design/decommissioning.md
 ##########
 @@ -0,0 +1,622 @@
+---
+title: Decommissioning in Ozone
+summary: Formal process to shut down machines in a safe way after the required replications.
+date: 2019-07-31
+jira: HDDS-1881
+status: current
+author: Anu Engineer, Marton Elek, Stephen O'Donnell
+---
+
+# Abstract
+
+The goal of decommissioning is to turn off a selected set of machines without data loss.
It may or may not require to move the existing replicas of the containers to other nodes.
+
+There are two main classes of the decommissioning:
+
+ * __Maintenance mode__: where the node is expected to be back after a while. It may not
require replication of containers if enough replicas are available from other nodes (as we
expect to have the current replicas after the restart.)
+
+ * __Decommissioning__: where the node won't be started again. All the data should be replicated
according to the current replication rules.
+
+Goals:
+
+ * Decommissioning can be canceled any time
+ * The progress of the decommissioning should be trackable
+ * The nodes under decommissioning / maintenance mode should not been used for new pipelines
/ containers
+ * The state of the datanodes should be persisted / replicated by the SCM (in HDFS the decommissioning
info exclude/include lists are replicated manually by the admin). If datanode is marked for
decommissioning this state be available after SCM and/or Datanode restarts.
+ * We need to support validations before decommissioing (but the violations can be ignored
by the admin).
+ * The administrator should be notified when a node can be turned off.
+ * The maintenance mode can be time constrained: if the node marked for maintenance for 1
week and the node is not up after one week, the containers should be considered as lost (DEAD
node) and should be replicated.
+
+# Introduction
+
+Ozone is a highly available file system that relies on commodity hardware. In other words,
Ozone is designed to handle failures of these nodes all the time.
+
+The Storage Container Manager(SCM) is designed to monitor the node health and replicate blocks
and containers as needed.
+
+At times, Operators of the cluster can help the SCM by giving it hints. When removing a datanode,
the operator can provide a hint. That is, a planned failure of the node is coming up, and
SCM can make sure it reaches a safe state to handle this planned failure.
+
+Some times, this failure is transient; that is, the operator is taking down this node temporarily.
In that case, we can live with lower replica counts by being optimistic.
+
+Both of these operations, __Maintenance__, and __Decommissioning__ are similar from the Replication
point of view. In both cases, and the user instructs us on how to handle an upcoming failure.
+
+Today, SCM (*Replication Manager* component inside SCM) understands only one form of failure
handling. This paper extends Replica Manager failure modes to allow users to request which
failure handling model to be adopted(Optimistic or Pessimistic).
+
+Based on physical realities, there are two responses to any perceived failure, to heal the
system by taking corrective actions or ignore the failure since the actions in the future
will heal the system automatically.
 
 Review comment:
   Based on these physical realities
 
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Issue Time Tracking
-------------------

    Worklog Id:     (was: 303053)
    Time Spent: 42.5h  (was: 42h 20m)

> Design doc: decommissioning in Ozone
> ------------------------------------
>
>                 Key: HDDS-1881
>                 URL: https://issues.apache.org/jira/browse/HDDS-1881
>             Project: Hadoop Distributed Data Store
>          Issue Type: Sub-task
>            Reporter: Elek, Marton
>            Assignee: Elek, Marton
>            Priority: Major
>              Labels: design, pull-request-available
>          Time Spent: 42.5h
>  Remaining Estimate: 0h
>
> Design doc can be attached to the documentation. In this jira the design doc will be
attached and merged to the documentation page.



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