docs: documentation for gcs metadata tuning (#844)

* changes

* changes

docs/ui/prepare-migration/end-migration.md

@@ -3,7 +3,7 @@ layout: default
 title: End Migration
 parent: Prepare Migration Page
 grand_parent: SMT UI
-nav_order: 8
+nav_order: 9
 ---
 
 # End migration

docs/ui/prepare-migration/gcs-metadata-path.md

@@ -0,0 +1,16 @@
+---
+layout: default
+title: GCS Metadata Path (Optional)
+parent: Prepare Migration Page
+grand_parent: SMT UI
+nav_order: 7
+---
+
+# GCS Metadata Path (Optional)
+{: .no_toc }
+
+{: .important }
+
+In case of minimal downtime sharded migration, for each shard, the Datastream jobs launched by the Spanner Migration Tool write data to a destination path on Google Cloud Storage. To store the metadata information such as session file, a new GCS Bucket is hence created. If the user does not wish for a new GCS Bucket to be created or wishes to name the bucket created, then the **GCS Metadata Path** Parameter can be set **optionally**.
+
+![](https://services.google.com/fh/files/misc/gcs-bucket-metadata.png)

docs/ui/prepare-migration/monitor.md

@@ -3,7 +3,7 @@ layout: default
 title: Monitoring
 parent: Prepare Migration Page
 grand_parent: SMT UI
-nav_order: 7
+nav_order: 8
 ---
 
 # Monitoring