DOC-13173 Enhance documentation for Index Rebalance and Upgrade

modules/ROOT/nav.adoc

@@ -69,6 +69,7 @@ include::third-party:partial$nav.adoc[]
  ** xref:learn:clusters-and-availability/size-limitations.adoc[Size Limits]
  ** xref:learn:clusters-and-availability/nodes.adoc[Nodes]
   *** xref:learn:clusters-and-availability/rebalance.adoc[Rebalance]
+   **** xref:learn:clusters-and-availability/rebalance-and-index-service.adoc[Index Rebalance]
   *** xref:learn:clusters-and-availability/removal.adoc[Removal]
   *** xref:learn:clusters-and-availability/failover.adoc[Failover]
    **** xref:learn:clusters-and-availability/graceful-failover.adoc[Graceful]

modules/install/pages/upgrade-feature-availability.adoc

@@ -22,7 +22,7 @@ _Not usable in mixed mode_ indicates that cluster-upgrade must be fully complete
 |===
 | Feature | Whether Usable in Mixed Mode
 
-| xref:learn:clusters-and-availability/rebalance.adoc#index-rebalance-methods[File-based Index Rebalancing]
+| xref:learn:clusters-and-availability/rebalance-and-index-service.adoc#index-rebalance-methods[]
 | You cannot enable file-based index rebalancing until all nodes have upgraded to version 7.6 or later. 
 
 | xref:learn:data/scopes-and-collections.adoc[Scopes & Collections]

modules/introduction/partials/new-features-76.adoc

@@ -150,7 +150,7 @@ See xref:manage:monitor/set-up-prometheus-for-monitoring.adoc[Configure Promethe
 
 * You can choose to have the rebalance process move an index's files between nodes instead of rebuilding them from scratch.
 This setting improves rebalance performance as moving the files is faster than rebuilding them.
-See xref:learn:clusters-and-availability/rebalance.adoc#index-rebalance-methods[Index Rebalance Methods].
+See xref:learn:clusters-and-availability/rebalance-and-index-service.adoc#index-rebalance-methods[].
 
 === Search Service
 

modules/introduction/partials/new-features-76_2.adoc

@@ -63,7 +63,7 @@ For details, see xref:n1ql:n1ql-language-reference/createindex.adoc[CREATE INDEX
 * In Couchbase Server Versions 7.6.0 and 7.6.1, enabling file-based index rebalance prevented you from controlling which Index Service nodes contain an index. 
 Version 7.6.2 removes this restriction.
 You can now use the `WITH <node>` clause of the `CREATE INDEX` {sqlpp} statement when your cluster has file-based index rebalancing enabled.
-See xref:learn:clusters-and-availability/rebalance.adoc#index-rebalance-methods[Index Rebalance Methods] for more information.
+See xref:learn:clusters-and-availability/rebalance-and-index-service.adoc#index-rebalance-methods[] for more information.
 +
 NOTE: You still cannot use the `WITH <node>` clause with the `ALTER INDEX` statement when your cluster has file-based index rebalancing enabled.
 

modules/learn/pages/clusters-and-availability/failover.adoc

@@ -27,9 +27,11 @@ Graceful failover _must_ be manually initiated. Hard failover _can_ be manually
 Hard failover can also be initiated automatically by Couchbase Server: this is known as _automatic_ failover.
 The Cluster Manager detects the unavailability of a node, and duly initiates a _hard_ failover, without administrator intervention.
 
-
-Note that when a node is failed over (as opposed to _removed_), some replica vBuckets are lost from the surviving nodes; since some are promoted to _active_ status, and are not replaced with new replica-copies.
-By contrast, xref:learn:clusters-and-availability/removal.adoc[removal] creates new copies of those replica vBuckets that would otherwise be lost. This maintains the cluster's previous level of data-availability; but results in greater competition for memory resources, across the surviving nodes.
+NOTE: When a node is failed over, some replica vBuckets on the remaining nodes are promoted to active status but are not recreated as new replicas.
+As a result, the cluster temporarily loses those replica copies.
++
+In contrast, when a node is removed, the cluster automatically restores any replica vBuckets that would otherwise be lost during xref:learn:clusters-and-availability/removal.adoc[removal].
+This preserves the cluster’s data availability level, but increases memory resource usage on the surviving nodes.
 
 Ideally, after any failover, xref:learn:clusters-and-availability/rebalance.adoc[rebalance] should be performed.
 This is especially important when a Data Service node has been failed over, since the rebalance will ensure an optimal ratio of active to replica vBuckets across all the remaining Data Service nodes.
@@ -180,7 +182,6 @@ For example, Couchbase Server considers a node running Analytics, Indexing, and
 If one is available, Couchbase Service always chooses an the cluster's xref:learn:clusters-and-availability/cluster-manager.adoc#master-services[Master Services] to host the active Master Service.
 Arbiter nodes do not run any services, and are therefore perfect candidates for hosting the Master Service.
 
-
 [#node-removal]
 == Node Removal