[GitHub] [ozone] GeorgeJahad commented on a change in pull request #2527: HDDS-5601. Publish upgrade documentation on Ozone website.

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GeorgeJahad commented on a change in pull request #2527:
URL: https://github.com/apache/ozone/pull/2527#discussion_r689676556



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File path: hadoop-hdds/docs/content/feature/Nonrolling-Upgrade.md
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+---
+title: Non-rolling upgrades and downgrades
+summary: Steps to do a non rolling upgrade of Ozone.
+date: 2021-02-15
+author: Aravindan Vijayan 
+menu:
+   main:
+      parent: Features
+summary: How to do non-rolling upgrades and downgrades of Ozone
+---
+<!--
+  Licensed 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. See accompanying LICENSE file.
+-->
+
+Ozone supports non-rolling upgrades and downgrades, where all components are stopped first, and then restarted with the upgraded or downgraded versions.
+
+## Upgrade States
+
+After upgrading components, the upgrade process is divided into two states:
+
+1. **Pre-finalized**: When the current components are stopped and the new versions are started, they will see that the data on disk was written by a previous version of Ozone and enter a pre-finalized state. In the pre-finalized state:
+    - The cluster can be downgraded at any time by stopping all components and restarting with the old versions.
+    - Backwards incompatible features introduced in the new version will be disallowed by the cluster.
+    - The cluster will remain fully operational with all functionality present in the old version still allowed.
+    - Any data created while pre-finalized will remain readable after downgrade.
+
+2. **Finalized**: When a finalize command is given to OM or SCM, they will enter a finalized state.  In the finalized state:
+    - The cluster can no longer be downgraded.
+    - All new features of the cluster introduced in the new version can be used.
+
+### Querying finalization status
+
+**OM**: `ozone admin om finalizationstatus`. If using OM HA, finalization status is checked for the quorum, not individual OMs.
+
+**SCM**: `ozone admin scm finalizationstatus`. SCM will report that finalization is complete once it has finalized and is aware of enough finalized datanodes to form a write pipeline. The remaining datanodes will finalize asynchronously and be incorporated into write pipelines after informing SCM that they have finalized.
+
+**Datanodes**: `ozone admin datanode list` will list all datanodes and their health state as seen by SCM. If SCM is finalized, then datanodes whose health state is `HEALTHY` have informed SCM that they have finalized. Datanodes whose health state is `HEALTHY_READONLY` have not yet informed SCM that they have finished finalization. `HEALTHY_READONLY` (pre-finalized) datanodes remain readable, so the cluster is operational even if some otherwise healthy datanodes have not yet finalized. `STALE` or `DEAD` datanodes will be told to finalize by SCM once they are reachable again.
+
+
+## Steps to upgrade and downgrade
+
+Starting with your current version of Ozone, complete the following steps to upgrade to a newer version of Ozone.
+
+1. If using OM HA and currently running Ozone 1.2.0 or greater, prepare the Ozone Manager.
+    ```
+    ozone admin om -id=<om-sevice-id> prepare
+    ```
+    If OM HA is not being used, this step can be skipped. This will block the Ozone Managers from receiving all write requests. See [Ozone Manager Prepare For Upgrade]({{< relref "../design/omprepare.md" >}}) for more information
+
+2.  Stop all components.
+
+3. Replace artifacts of all components with the newer versions.
+
+4. Start the components
+    1. Start the SCM and datanodes as usual:
+        ```
+        ozone --daemon scm start
+        ```
+        ```
+        ozone --daemon datanode start
+        ```
+
+    2. Start the Ozone Manager using the `--upgrade` flag to take it out of prepare mode.
+        ```
+        ozone --daemon om start --upgrade
+        ```
+        - There also exists a `--downgrade` flag which is an alias of `--upgrade`. The name used does not matter.
+
+        - **IMPORTANT**: All OMs must be started with the `--upgrade`  or `--downgrade` flag in this step. If some or none of the OMs are started with this flag by mistake, run `ozone admin om -id=<om-sevice-id> cancelprepare` to make sure all OMs leave prepare mode.

Review comment:
       This phrase seems weird: " If some or none of the OMs".  Should that just be: "If some of the OMs"?




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