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new 2ae8d6da28 HDDS-13379. Document SCM Safe Mode and its configuration
properties. (#8737)
2ae8d6da28 is described below
commit 2ae8d6da2849286b044e9877a90fdd919c3653c4
Author: Wei-Chiu Chuang <[email protected]>
AuthorDate: Wed Jul 9 18:16:20 2025 -0700
HDDS-13379. Document SCM Safe Mode and its configuration properties. (#8737)
Generated-by: Google Gemini 2.5 Pro/Flash, + Gemini Cli
---
.../docs/content/concept/StorageContainerManager.md | 21 +++++++++++++++++++++
1 file changed, 21 insertions(+)
diff --git a/hadoop-hdds/docs/content/concept/StorageContainerManager.md
b/hadoop-hdds/docs/content/concept/StorageContainerManager.md
index 48d509016a..00aa7d0d38 100644
--- a/hadoop-hdds/docs/content/concept/StorageContainerManager.md
+++ b/hadoop-hdds/docs/content/concept/StorageContainerManager.md
@@ -87,6 +87,27 @@ The following data is persisted in Storage Container Manager
side in a specific
* Valid cert
* Used by the internal Certificate Authority to authorize other Ozone
services
+## Safe Mode
+
+SCM (Storage Container Manager) enters safe mode on startup. This is a
protective state that allows the system to become stable before it becomes
fully operational. During safe mode, certain operations like block allocation
are restricted.
+
+### How to Exit Safe Mode
+
+There are two ways to exit safe mode:
+
+1. **Automatic Exit:** SCM will automatically exit safe mode when a set of
predefined `SafeModeExitRule`s are satisfied. These rules ensure that the
cluster is in a healthy state. The primary rules are:
+ * **`DataNodeSafeModeRule`**: Checks if a minimum number of DataNodes
have registered with the SCM. This is configured by
`hdds.scm.safemode.min.datanode` (default: `3`).
+ * **`RatisContainerSafeModeRule`**: Checks if a certain percentage of
containers with at least one replica reported are available. This is configured
by `hdds.scm.safemode.threshold.pct` (default: `0.99`).
+ * **`HealthyPipelineSafeModeRule`**: Checks if a certain percentage of
pipelines are healthy. This is configured by
`hdds.scm.safemode.healthy.pipeline.pct` (default: `0.10`).
+ * **`OneReplicaPipelineSafeModeRule`**: Checks if a certain percentage
of pipelines have at least one replica reported. This is configured by
`hdds.scm.safemode.atleast.one.node.reported.pipeline.pct` (default: `0.90`).
+ * **`ECContainerSafeModeRule`**: Checks if a certain percentage of
erasure coded block groups are healthy. This is also configured by
`hdds.scm.safemode.threshold.pct` (default: `0.99`).
+
+2. **Manual Exit:** You can force SCM to exit safe mode using the `ozone
admin safemode --force-exit` command.
+
+### Safe Mode Pre-Check
+
+There's also a "pre-check" phase. SCM will not exit safe mode until all
pre-check rules are satisfied. The `DataNodeSafeModeRule` is a pre-check rule.
This means that SCM will wait for a minimum number of DataNodes to be available
before it even considers the other conditions for exiting safe mode.
+
## Notable configurations
key | default | description
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