szetszwo commented on code in PR #9580:
URL: https://github.com/apache/ozone/pull/9580#discussion_r2669448953
##########
hadoop-hdds/docs/content/feature/multi-raft-support.md:
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@@ -69,6 +69,64 @@ Ratis handles concurrent logs per node.
This property is effective only when the previous property is set to 0.
The value of this property must be greater than 0.
+### Calculating Ratis Pipeline Limits
+
+The target number of open, FACTOR_THREE Ratis pipelines is controlled by three
properties that define the maximum
+number of pipelines in the cluster at a cluster-wide level, datanode level,
and metadata disk level, respectively.
+SCM will create pipelines until the most restrictive limit is met.
+
+1. **Cluster-wide Limit (`ozone.scm.ratis.pipeline.limit`)**
+ * **Description**: An absolute, global limit for the total number of
open, FACTOR_THREE Ratis pipelines
+ across the entire cluster. This acts as a final cap on the total
number of pipelines.
+ * **Default Value**: `0` (which means no global limit is enforced by
default).
+
+2. **Datanode-level Fixed Limit (`ozone.scm.datanode.pipeline.limit`)**
+ * **Description**: When set to a positive number, this property defines
a fixed maximum number of pipelines for
+ every datanode. This is one of two ways to calculate a cluster-wide
target.
+ * **Default Value**: `2`
+ * **Calculation**: If this is set, the target is `(<this value> *
<number of healthy datanodes>) / 3`.
+
+3. **Datanode-level Dynamic Limit (`ozone.scm.pipeline.per.metadata.disk`)**
+ * **Description**: This property is used only when
`ozone.scm.datanode.pipeline.limit` is explicitly set to `0`.
+ It calculates a dynamic limit for each datanode based on its available
metadata disks.
+ * **Default Value**: `2`
+ * **Calculation**: The limit for each datanode is
+ `(<this value> * <number of metadata disks on that datanode>)`.
+ The total cluster-wide target is the sum of all individual datanode
limits, divided by 3.
Review Comment:
Remove this section since it seems not true (or I cannot find the code
enforcing it). I do see that the value is used for filtering datanodes.
https://github.com/apache/ozone/blob/4fd83602c3080a8174876bc9c19c356af857fd56/hadoop-hdds/server-scm/src/main/java/org/apache/hadoop/hdds/scm/pipeline/RatisPipelineProvider.java#L104-L131
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