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new 1159d9b7b45 HDDS-13369. [Docs] Maintenance mode. (#8728)
1159d9b7b45 is described below
commit 1159d9b7b4521f39cda716079fbaf4acb9c2d730
Author: Wei-Chiu Chuang <[email protected]>
AuthorDate: Thu Jul 10 18:43:40 2025 -0700
HDDS-13369. [Docs] Maintenance mode. (#8728)
Generated-by: Google Gemini Cli, Gemini 2.5 Flash
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hadoop-hdds/docs/content/feature/Maintenance.md | 78 +++++++++++++++++++++++++
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+---
+title: "Maintenance Mode"
+menu:
+ main:
+ parent: Features
+summary: Maintenance mode for Datanodes.
+---
+<!---
+ Licensed to the Apache Software Foundation (ASF) under one or more
+ contributor license agreements. See the NOTICE file distributed with
+ this work for additional information regarding copyright ownership.
+ The ASF licenses this file to You under the Apache License, Version 2.0
+ (the "License"); you may not use this file except in compliance with
+ the License. You may obtain a copy of the License at
+
+ http://www.apache.org/licenses/LICENSE-2.0
+
+ Unless required by applicable law or agreed to in writing, software
+ distributed under the License is distributed on an "AS IS" BASIS,
+ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ See the License for the specific language governing permissions and
+ limitations under the License.
+-->
+
+# DataNode Maintenance Mode
+
+Maintenance mode is a feature in Apache Ozone that allows you to temporarily
take a DataNode offline for maintenance operations (e.g., hardware upgrades,
software updates) without triggering immediate data replication. Unlike
decommissioning, which aims to permanently remove a DataNode and its data from
the cluster, maintenance mode is designed for temporary outages.
+
+While in maintenance mode, a DataNode does not accept new writes but may still
serve reads, assuming containers are healthy and online. Existing data on the
DataNode will remain in place, and replication of its data will only be
triggered if the DataNode remains in maintenance mode beyond a configurable
timeout period. This allows for planned downtime without unnecessary data
movement, reducing network overhead and cluster load.
+
+The DataNode transitions through the following operational states during
maintenance:
+
+1. **IN_SERVICE**: The DataNode is fully operational and participating in
data writes and reads.
+2. **ENTERING_MAINTENANCE**: The DataNode is transitioning into maintenance
mode. New writes will be avoided.
+3. **IN_MAINTENANCE**: The DataNode is in maintenance mode. Data will not be
written to it. If the DataNode remains in this state beyond the configured
maintenance window, its data will start to be replicated to other DataNodes to
ensure data durability.
+
+## Command Line Usage
+
+To place a DataNode into maintenance mode, use the `ozone admin datanode
maintenance` command. You can specify a duration for the maintenance period. If
no duration is specified, a default duration will be used (this can be
configured).
+
+To check the current state of the datanodes, including their operational
state, you can execute the following command:
+
+```shell
+ozone admin datanode list
+```
+
+To start maintenance mode for one or more DataNodes:
+
+```shell
+ozone admin datanode maintenance [-hV] [-id=<scmServiceId>] [--scm=<scm>]
[--end=<hours>] [--force] [<hosts>...]
+```
+- `<hosts>`: A space-separated list of hostnames or IP addresses of the
DataNodes to put into maintenance mode.
+- `--end=<hours>`: Optional. Automatically end maintenance after the given
hours. By default, maintenance must be ended manually.
+- `--force`: Optional. Forcefully try to put the datanode(s) into maintenance
mode.
+
+To take a DataNode out of maintenance mode and return it to `IN_SERVICE`
state, you can use the `recommission` command:
+
+```shell
+ozone admin datanode recommission [-hV] [-id=<scmServiceId>] [--scm=<scm>]
[<hosts>...]
+```
+
+## Configuration Properties
+
+The following properties, typically set in `ozone-site.xml`, are relevant to
maintenance mode:
+
+- `hdds.scm.replication.maintenance.replica.minimum`: The minimum number of
container replicas which must be available for a node to enter maintenance.
Default value is `2`. If putting a node into maintenance reduces the available
replicas for any container below this level, the node will remain in the
`ENTERING_MAINTENANCE` state until a new replica is created.
+- `hdds.scm.replication.maintenance.remaining.redundancy`: The number of
redundant containers in a group which must be available for a node to enter
maintenance. Default value is `1`. If putting a node into maintenance reduces
the redundancy below this value, the node will remain in the
`ENTERING_MAINTENANCE` state until a new replica is created. For Ratis
containers, the default value of 1 ensures at least two replicas are online,
meaning 1 more can be lost without data becoming unavail [...]
+
+## Metrics
+
+The following SCM metrics are relevant to DataNode maintenance mode:
+
+- `DecommissioningMaintenanceNodesTotal`: This metric reports the total number
of DataNodes that are currently in either decommissioning or maintenance mode.
+- `RecommissionNodesTotal`: This metric reports the total number of DataNodes
that are currently being recommissioned (i.e., returning to `IN_SERVICE` state
from either decommissioning or maintenance mode).
+
+## Reference
+
+For information on permanently removing a DataNode from the cluster, refer to
the [Decommissioning](decommission.html) user documentation.
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