Clarify NoteDb migration when upgrading to v2.16
Off-line reindex is mandatory when skipping releases and migrating from
Gerrit < 2.15.
NoteDb on-line and off-line migrations are still available beyond
2.15 and is mandatory for upgrading in the future to 3.0
Change-Id: I61105d3809608cc620005cce3b145806182e5a1c
diff --git a/pages/site/releases/2.16.md b/pages/site/releases/2.16.md
index 0af43c9..3cb8d4d 100644
--- a/pages/site/releases/2.16.md
+++ b/pages/site/releases/2.16.md
@@ -82,7 +82,22 @@
Note that it is not necessary to reindex the changes and accounts indexes
offline. These will automatically be reindexed by the online reindexer after
-starting Gerrit.
+starting Gerrit, assuming you were migrating from v2.15.
+
+### Migration to NoteDb
+
+NoteDb is the preferred storage for changes and you are strongly advised to
+migrate changes from ReviewDb when upgrading to Gerrit v2.16 from either v2.14
+or v2.15.
+
+See more information about the migration process to NoteDb in the Gerrit Documentation:
+
+- [On-line migration](https://gerrit-review.googlesource.com/Documentation/note-db.html#online-migration)
+- [Off-line migration](https://gerrit-review.googlesource.com/Documentation/note-db.html#offline-migration)
+
+**NOTE: ReviewDb is still technically available on Gerrit v2.16**.
+However, upgrade to NoteDb is strongly recommended, although not enforced during migration.
+The next version of Gerrit (v3.0) won't support ReviewDb anymore.
### Support for GWT UI is deprecated
