feat: OpenSearch BTAR

docs/platform/concepts/backup-to-another-region.md

@@ -5,6 +5,8 @@ sidebar_label: Backup to another region
 ---
 
 import RelatedPages from "@site/src/components/RelatedPages";
+import Tabs from '@theme/Tabs';
+import TabItem from '@theme/TabItem';
 
 In addition to the primary service backup, you can have a secondary backup in an alternative location.
 
@@ -19,27 +21,64 @@ region. BTAR can bolster data resilience and helps improve data protection again
 disasters in the primary backup region. When the primary region is down, BTAR allows
 forking the service from an additional copy of the backup residing in a secondary region.
 
-BTAR is supported for the following services:
+## Limitations
+
+- The cloud provider for your additional backup region must match the cloud provider for
+  your service and the primary backup.
+- Secondary backup can only be restored in the region where it was stored.
+
+### Supported services
+
+BTAR is only supported for the following service types:
 
 - Aiven for PostgreSQL®
 - Aiven for MySQL®
 - Aiven for OpenSearch®
 
+### Service-specific limitations
+
+<Tabs groupId="group1">
+<TabItem value="sql-relational" label="PostgreSQL & MySQL" default>
+
+- To
+  [restore your service from an additional backup](/docs/platform/howto/btar/manage-backup-to-another-region)
+  using point-in-time recovery (PITR), set up the time to no earlier than the time of
+  taking the oldest replicated base backup.
+- Secondary backup is generated only after a primary backup is complete, and there might
+  be a data replication lag between the primary region and the secondary region.
+
+</TabItem>
+<TabItem value="non-sql-search-analytics" label="OpenSearch">
+
+- The synchronization of snapshots between the regions works only for base snapshots created
+  after the BTAR activation.
+- Point-in-time recovery (PITR) is not supported for
+  [restoring your service from an additional backup](/docs/platform/howto/btar/manage-backup-to-another-region).
+- Although a base snapshot in the primary region and its corresponding BTAR snapshot in
+  the secondary region are generated at the same time, there might be some negligible data
+  discrepancies between them.
+
+</TabItem>
+</Tabs>
+
 ## How BTAR works
 
-When you enable the backup to another region (BTAR) feature, an additional service backup
-is created in the cloud region of your choice that is alternative to the primary backup
+When you enable the backup to another region (BTAR) feature, additional service backups
+are created in the cloud region of your choice that is alternative to the primary backup
 location.
 
+Restoring from a secondary backup, for example in case of an outage of the primary region,
+can be done by creating a fork of the service in the region where the secondary backup is
+located.
+
+<Tabs groupId="group1">
+<TabItem value="sql-relational" label="PostgreSQL & MySQL" default>
+
 Secondary backups are generated from primary backups, not from the service itself. For
 this reason, your secondary backup becomes available only after the primary backup is
 taken. There might be a data replication lag between the primary region and the secondary
 region.
 
-Restoring from a secondary backup, for example in case of an outage of the primary region,
-can be done by creating a fork of the service in the region where the secondary backup is
-located.
-
 ```mermaid
 flowchart LR
     subgraph Primary_region
@@ -50,7 +89,6 @@ flowchart LR
             direction LR
             PB1
             PB2
-            PB3
             PBn
             end
         end
@@ -62,28 +100,62 @@ flowchart LR
             direction LR
             SB1
             SB2
-            SB3
             SBn
             end
         end
-    Service_X -- Default \n backups --> Primary_backups
-    Primary_backups -- Cross-region backups \n if BTAR  enabled --> Secondary_backups
-    Secondary_backups -- Secondary backups \n to restore service X --> Forked_service_X
-    Service_X -- Forking service X \n if primary region down --> Forked_service_X
+    Service_X -- Base backups<br/>by default --> Primary_backups
+    Primary_backups -- Cross-region backups<br/>if BTAR  enabled --> Secondary_backups
+    Secondary_backups -- Secondary backups<br/>to restore service X --> Forked_service_X
+    Service_X -- Forking service X<br/>if primary region down --> Forked_service_X
 ```
 
-## Limitations
+</TabItem>
+<TabItem value="non-sql-search-analytics" label="OpenSearch">
 
-- BTAR is supported for Aiven for MySQL®, Aiven for PostgreSQL®, and Aiven for OpenSearch®.
-- The cloud provider for your additional backup region must match the cloud provider for
-  your service and the primary backup.
-- To
-  [restore your service from an additional backup](/docs/platform/howto/btar/manage-backup-to-another-region)
-  using point-in-time recovery (PITR), set up the time to no earlier than the time of
-  taking the oldest replicated base backup.
-- Secondary backup can only be restored in the region where it was stored.
-- Secondary backup is generated only after a primary backup is complete, and there might
-  be a data replication lag between the primary region and the secondary region.
+An additional snapshot repository is created in the secondary region. In this repository,
+BTAR snapshots are generated directly from the service. They are created and managed in
+synchronization with
+[base snapshots](/docs/products/opensearch/howto/manage-snapshots)
+in the primary region using the
+[native OpenSearch API](https://docs.opensearch.org/latest/api-reference/snapshots/index/).
+For example, when a
+[base snapshot is created](/docs/products/opensearch/howto/manage-snapshots#create-a-snapshot)
+in the primary region, its BTAR counterpart is created simultaneously with an identical
+name in the secondary region.
+
+```mermaid
+flowchart LR
+    subgraph Primary_region
+        direction LR
+        subgraph Primary_backups
+            direction TB
+            PB1
+            PB2
+            PBn
+            end
+        subgraph Service_X
+            end
+        end
+    subgraph Secondary_region
+        direction LR
+        subgraph Forked_service_X
+            end
+        subgraph Secondary_backups
+            direction TB
+            SB1
+            SB2
+            SBn
+            end
+        end
+    Service_X -- Base backups<br/>by default --> Primary_backups
+    Service_X -- Cross-region backups<br/>if BTAR enabled --> Secondary_backups
+    Secondary_backups -- Secondary backups<br/>to restore service X --> Forked_service_X
+    Service_X -- Forking service X<br/>if primary region down --> Forked_service_X
+
+```
+
+</TabItem>
+</Tabs>
 
 <RelatedPages/>