chore: apply suggestions from CR

docs/nightly/en/user-guide/operations/configuration.md

@@ -565,6 +565,11 @@ store_addr = "127.0.0.1:2379"
 selector = "LeaseBased"
 # Store data in memory, false by default.
 use_memory_store = false
+## Whether to enable region failover.
+## This feature is only available on GreptimeDB running on cluster mode and
+## - Using Remote WAL
+## - Using shared storage (e.g., s3).
+enable_region_failover = false
 
 [wal]
 # Available wal providers:
@@ -617,6 +622,7 @@ backoff_deadline = "5mins"
 | `enable_telemetry`         | Bool    | `true`                 | Whether to enable greptimedb telemetry.                                                                                                                                       |
 | `store_key_prefix`         | String  | `""`                   | If it's not empty, the metasrv will store all data with this key prefix.                                                                                                      |
 | `enable_region_failover`   | Bool    | `false`                | Whether to enable region failover.<br/>This feature is only available on GreptimeDB running on cluster mode and<br/>- Using Remote WAL<br/>- Using shared storage (e.g., s3). |
+| `enable_region_failover`   | Bool    | `false`                | Whether to enable region failover.<br/>This feature is only available on GreptimeDB running on cluster mode and<br/>- Using Remote WAL<br/>- Using shared storage (e.g., s3). |
 | `wal`                      | --      | --                     | --                                                                                                                                                                            |
 | `wal.provider`             | String  | `raft_engine`          | --                                                                                                                                                                            |
 | `wal.broker_endpoints`     | Array   | --                     | The broker endpoints of the Kafka cluster.                                                                                                                                    |

docs/nightly/en/user-guide/operations/region-failover.md

@@ -1,36 +1,55 @@
 # Region Failover
 
-Region Failover provides the ability to recover regions from crashed Datanodes without losing data.
+Region Failover provides the ability to recover regions from crashed Datanodes without losing data. This is implemented via [Region Migration](/user-guide/operations/region-migration).
+
+## Enable the Region Failover
 
 :::warning Warning
 This feature is only available on GreptimeDB running on cluster mode and
 
 - Using Kafka WAL
 - Using [shared storage](/user-guide/operations/configuration.md#storage-options) (e.g., AWS S3)
-
 :::
 
-## The Recovery Time of Region Failover
+### Via configuration file
+Set the `enable_region_failover=true` in [metasrv](/user-guide/operations/configuration.md#metasrv-only-configuration) configuration file.
 
-:::tip Note
+### Via GreptimeDB Operator
 
-In best practices, the number of topics/partitions supported by a Kafka cluster is limited (exceeding this number can degrade Kafka cluster performance). Therefore, we allow multiple regions to share a single topic as the WAL.
-:::
+Set the `meta.enableRegionFailover=true`, e.g.,
+```bash
+helm install greptimedb greptime/greptimedb-cluster \
+  --set meta.enableRegionFailover=true \ 
+  ...
+```
+
+## The recovery time of Region Failover
 
-The Recovery Time of Region Failover depends on:
+The recovery time of Region Failover depends on:
 
 - number of regions per Topic.
 - the Kafka cluster read throughput performance.
 
+:::tip Note
+
+In best practices, the number of topics/partitions supported by a Kafka cluster is limited (exceeding this number can degrade Kafka cluster performance). Therefore, we allow multiple regions to share a single topic as the WAL.
+:::
+
 ### The read amplification
 
-However, the cost of multiple regions to share a single topic is read amplification during replaying WAL.
+The data belonging to a specific region consists of data files plus data in the WAL (typically `WAL[LastCheckpoint...Latest]`). If multiple regions share a single topic, replaying data for a specific region from the Topic requires filtering out unrelated data (i.e., data from other regions). **This means reading more data than the actual data size of the region, a phenomenon known as read amplification**.
+
+Although multiple regions share the same topic, allowing the Datanode to support more regions, the cost of this approach is read amplification during WAL replay.
 
 For example, configure 128 topics for [metasrv](/user-guide/operations/configuration.md#metasrv-only-configuration), and if the whole cluster holds 1024 regions (physical regions), every 8 regions will share one topic.
 
 ![Read Amplification](/remote-wal-read-amplification.png)
 
-<p style="text-align: center;"><b>(Figure1: recovery Region 0 need to read 7 times the redundant data)</b></p>
+<p style="text-align: center;"><b>(Figure1: recovery Region 3 need to read 7 times the redundant data)</b></p>
+
+:::warning Note
+In actual scenarios, the reading amplification may be larger than this model.
+:::
 
 A simple model to estimate the read amplification factor:
 
@@ -47,7 +66,7 @@ A simple model to estimate the read amplification factor:
 
 **If the Kafka cluster can provide 300MB/s read throughput, recovering 100 regions requires approximately 10 minutes (182.5GB/0.3GB = 10m).**
 
-### Examples
+### More examples
 
 | Number of regions per Topic | Replay size (GB) | Kafka throughput 300MB/s- Reovery time (secs) | Kafka throughput 1000MB/s- Reovery time (secs) |
 | --------------------------- | ---------------- | --------------------------------------------- | ---------------------------------------------- |