diff --git a/gerrit-acceptance-framework/src/test/java/com/google/gerrit/acceptance/GerritServer.java b/gerrit-acceptance-framework/src/test/java/com/google/gerrit/acceptance/GerritServer.java
index 52dc4f2..2b13df0 100644
--- a/gerrit-acceptance-framework/src/test/java/com/google/gerrit/acceptance/GerritServer.java
+++ b/gerrit-acceptance-framework/src/test/java/com/google/gerrit/acceptance/GerritServer.java
@@ -61,6 +61,14 @@
 import org.eclipse.jgit.util.FS;
 
 public class GerritServer implements AutoCloseable {
+  public static class StartupException extends Exception {
+    private static final long serialVersionUID = 1L;
+
+    StartupException(String msg, Throwable cause) {
+      super(msg, cause);
+    }
+  }
+
   @AutoValue
   public abstract static class Description {
     public static Description forTestClass(
@@ -301,7 +309,12 @@
               }
               return null;
             });
-    serverStarted.await();
+    try {
+      serverStarted.await();
+    } catch (BrokenBarrierException e) {
+      daemon.stop();
+      throw new StartupException("Failed to start Gerrit daemon; see log", e);
+    }
     System.out.println("Gerrit Server Started");
 
     return new GerritServer(desc, createTestInjector(daemon), daemon, daemonService);
diff --git a/gerrit-acceptance-framework/src/test/java/com/google/gerrit/acceptance/StandaloneSiteTest.java b/gerrit-acceptance-framework/src/test/java/com/google/gerrit/acceptance/StandaloneSiteTest.java
new file mode 100644
index 0000000..be34ba6
--- /dev/null
+++ b/gerrit-acceptance-framework/src/test/java/com/google/gerrit/acceptance/StandaloneSiteTest.java
@@ -0,0 +1,142 @@
+// Copyright (C) 2017 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gerrit.acceptance;
+
+import static com.google.common.truth.Truth.assertThat;
+import static java.util.stream.Collectors.joining;
+import static org.junit.Assert.fail;
+
+import com.google.common.collect.Streams;
+import com.google.gerrit.launcher.GerritLauncher;
+import com.google.gerrit.reviewdb.client.Account;
+import com.google.gerrit.reviewdb.server.ReviewDb;
+import com.google.gerrit.server.CurrentUser;
+import com.google.gerrit.server.config.SitePaths;
+import com.google.gerrit.server.util.ManualRequestContext;
+import com.google.gerrit.server.util.OneOffRequestContext;
+import com.google.gerrit.server.util.RequestContext;
+import com.google.gerrit.testutil.ConfigSuite;
+import com.google.inject.Injector;
+import com.google.inject.Provider;
+import java.util.Arrays;
+import org.eclipse.jgit.lib.Config;
+import org.junit.Rule;
+import org.junit.rules.RuleChain;
+import org.junit.rules.TemporaryFolder;
+import org.junit.rules.TestRule;
+import org.junit.runner.Description;
+import org.junit.runner.RunWith;
+import org.junit.runners.model.Statement;
+
+@RunWith(ConfigSuite.class)
+@UseLocalDisk
+public abstract class StandaloneSiteTest {
+  protected class ServerContext implements RequestContext, AutoCloseable {
+    private final GerritServer server;
+    private final ManualRequestContext ctx;
+
+    private ServerContext(GerritServer server) throws Exception {
+      this.server = server;
+      Injector i = server.getTestInjector();
+      if (adminId == null) {
+        adminId = i.getInstance(AccountCreator.class).admin().getId();
+      }
+      ctx = i.getInstance(OneOffRequestContext.class).openAs(adminId);
+    }
+
+    @Override
+    public CurrentUser getUser() {
+      return ctx.getUser();
+    }
+
+    @Override
+    public Provider<ReviewDb> getReviewDbProvider() {
+      return ctx.getReviewDbProvider();
+    }
+
+    public Injector getInjector() {
+      return server.getTestInjector();
+    }
+
+    @Override
+    public void close() throws Exception {
+      try {
+        ctx.close();
+      } finally {
+        server.close();
+      }
+    }
+  }
+
+  @ConfigSuite.Parameter public Config baseConfig;
+  @ConfigSuite.Name private String configName;
+
+  private final TemporaryFolder tempSiteDir = new TemporaryFolder();
+
+  private final TestRule testRunner =
+      new TestRule() {
+        @Override
+        public Statement apply(Statement base, Description description) {
+          return new Statement() {
+            @Override
+            public void evaluate() throws Throwable {
+              beforeTest(description);
+              base.evaluate();
+            }
+          };
+        }
+      };
+
+  @Rule public RuleChain ruleChain = RuleChain.outerRule(tempSiteDir).around(testRunner);
+
+  protected SitePaths sitePaths;
+
+  private GerritServer.Description serverDesc;
+  private Account.Id adminId;
+
+  private void beforeTest(Description description) throws Exception {
+    serverDesc = GerritServer.Description.forTestMethod(description, configName);
+    sitePaths = new SitePaths(tempSiteDir.getRoot().toPath());
+    GerritServer.init(serverDesc, baseConfig, sitePaths.site_path);
+  }
+
+  protected ServerContext startServer() throws Exception {
+    return new ServerContext(startImpl());
+  }
+
+  protected void assertServerStartupFails() throws Exception {
+    try (GerritServer server = startImpl()) {
+      fail("expected server startup to fail");
+    } catch (GerritServer.StartupException e) {
+      // Expected.
+    }
+  }
+
+  private GerritServer startImpl() throws Exception {
+    return GerritServer.start(serverDesc, baseConfig, sitePaths.site_path);
+  }
+
+  protected static void runGerrit(String... args) throws Exception {
+    assertThat(GerritLauncher.mainImpl(args))
+        .named("gerrit.war " + Arrays.stream(args).collect(joining(" ")))
+        .isEqualTo(0);
+  }
+
+  @SafeVarargs
+  protected static void runGerrit(Iterable<String>... multiArgs) throws Exception {
+    runGerrit(
+        Arrays.stream(multiArgs).flatMap(args -> Streams.stream(args)).toArray(String[]::new));
+  }
+}
diff --git a/gerrit-acceptance-tests/src/test/java/com/google/gerrit/acceptance/pgm/OfflineNoteDbMigrationIT.java b/gerrit-acceptance-tests/src/test/java/com/google/gerrit/acceptance/pgm/OfflineNoteDbMigrationIT.java
index 1676f3e..9b36b03 100644
--- a/gerrit-acceptance-tests/src/test/java/com/google/gerrit/acceptance/pgm/OfflineNoteDbMigrationIT.java
+++ b/gerrit-acceptance-tests/src/test/java/com/google/gerrit/acceptance/pgm/OfflineNoteDbMigrationIT.java
@@ -17,48 +17,36 @@
 import static com.google.common.truth.Truth.assertThat;
 import static com.google.common.truth.Truth8.assertThat;
 
+import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
-import com.google.gerrit.acceptance.AccountCreator;
-import com.google.gerrit.acceptance.GerritServer;
 import com.google.gerrit.acceptance.NoHttpd;
-import com.google.gerrit.acceptance.TestAccount;
-import com.google.gerrit.acceptance.UseLocalDisk;
+import com.google.gerrit.acceptance.StandaloneSiteTest;
 import com.google.gerrit.extensions.api.GerritApi;
 import com.google.gerrit.extensions.common.ChangeInput;
-import com.google.gerrit.launcher.GerritLauncher;
-import com.google.gerrit.reviewdb.client.Account;
 import com.google.gerrit.reviewdb.client.Change;
 import com.google.gerrit.reviewdb.client.Project;
 import com.google.gerrit.reviewdb.client.RefNames;
 import com.google.gerrit.reviewdb.server.ReviewDb;
-import com.google.gerrit.reviewdb.server.ReviewDbUtil;
-import com.google.gerrit.server.config.SitePaths;
 import com.google.gerrit.server.git.GitRepositoryManager;
+import com.google.gerrit.server.index.GerritIndexStatus;
+import com.google.gerrit.server.index.change.ChangeSchemaDefinitions;
 import com.google.gerrit.server.notedb.ConfigNotesMigration;
 import com.google.gerrit.server.notedb.NoteDbChangeState;
 import com.google.gerrit.server.notedb.NoteDbChangeState.PrimaryStorage;
 import com.google.gerrit.server.notedb.NoteDbChangeState.RefState;
 import com.google.gerrit.server.notedb.NotesMigrationState;
-import com.google.gerrit.server.util.ManualRequestContext;
-import com.google.gerrit.server.util.OneOffRequestContext;
-import com.google.gerrit.testutil.ConfigSuite;
-import com.google.gerrit.testutil.TempFileUtil;
-import com.google.inject.Injector;
-import java.nio.file.Path;
-import java.util.stream.Stream;
-import org.eclipse.jgit.lib.Config;
+import com.google.gerrit.server.schema.ReviewDbFactory;
+import com.google.gwtorm.server.SchemaFactory;
+import com.google.inject.Key;
+import com.google.inject.TypeLiteral;
 import org.eclipse.jgit.lib.ObjectId;
 import org.eclipse.jgit.lib.Ref;
 import org.eclipse.jgit.lib.Repository;
 import org.eclipse.jgit.lib.StoredConfig;
 import org.eclipse.jgit.storage.file.FileBasedConfig;
 import org.eclipse.jgit.util.FS;
-import org.junit.After;
 import org.junit.Before;
-import org.junit.Rule;
 import org.junit.Test;
-import org.junit.rules.TestWatcher;
-import org.junit.runner.Description;
 
 /**
  * Tests for offline {@code migrate-to-note-db} program.
@@ -67,119 +55,115 @@
  * adding tests to {@link com.google.gerrit.acceptance.server.notedb.OnlineNoteDbMigrationIT} if
  * possible.
  */
-@UseLocalDisk
 @NoHttpd
-public class OfflineNoteDbMigrationIT {
-  @Rule
-  public TestWatcher testWatcher =
-      new TestWatcher() {
-        @Override
-        protected void starting(Description description) {
-          serverDesc = GerritServer.Description.forTestMethod(description, ConfigSuite.DEFAULT);
-        }
-      };
-
-  private GerritServer.Description serverDesc;
-
-  private Path site;
+public class OfflineNoteDbMigrationIT extends StandaloneSiteTest {
   private StoredConfig gerritConfig;
 
+  private Project.NameKey project;
+  private Change.Id changeId;
+
   @Before
   public void setUp() throws Exception {
-    site = TempFileUtil.createTempDirectory().toPath();
-    GerritServer.init(serverDesc, new Config(), site);
-    gerritConfig = new FileBasedConfig(new SitePaths(site).gerrit_config.toFile(), FS.detect());
-  }
-
-  @After
-  public void tearDown() throws Exception {
-    TempFileUtil.cleanup();
-  }
-
-  @Test
-  public void rebuildEmptySiteStartingWithNoteDbDisabed() throws Exception {
-    assertNotesMigrationState(NotesMigrationState.REVIEW_DB);
-    migrate();
-    assertNotesMigrationState(NotesMigrationState.READ_WRITE_NO_SEQUENCE);
-  }
-
-  @Test
-  public void rebuildEmptySiteStartingWithNoteDbEnabled() throws Exception {
-    setNotesMigrationState(NotesMigrationState.READ_WRITE_NO_SEQUENCE);
-    migrate();
-    assertNotesMigrationState(NotesMigrationState.READ_WRITE_NO_SEQUENCE);
+    gerritConfig = new FileBasedConfig(sitePaths.gerrit_config.toFile(), FS.detect());
   }
 
   @Test
   public void rebuildOneChangeTrialMode() throws Exception {
     assertNotesMigrationState(NotesMigrationState.REVIEW_DB);
-    Project.NameKey project = new Project.NameKey("project");
+    setUpOneChange();
 
-    Account.Id accountId;
-    Change.Id id;
-    try (GerritServer server = startServer();
-        ManualRequestContext ctx = openContext(server)) {
-      accountId = ctx.getUser().getAccountId();
-      GerritApi gApi = server.getTestInjector().getInstance(GerritApi.class);
-      gApi.projects().create("project");
-
-      ChangeInput in = new ChangeInput(project.get(), "master", "Test change");
-      in.newBranch = true;
-      id = new Change.Id(gApi.changes().create(in).info()._number);
-    }
-
-    migrate("--trial");
+    migrate();
     assertNotesMigrationState(NotesMigrationState.READ_WRITE_NO_SEQUENCE);
 
-    try (GerritServer server = startServer();
-        ManualRequestContext ctx = openContext(server, accountId)) {
-      GitRepositoryManager repoManager =
-          server.getTestInjector().getInstance(GitRepositoryManager.class);
+    try (ServerContext ctx = startServer()) {
+      GitRepositoryManager repoManager = ctx.getInjector().getInstance(GitRepositoryManager.class);
       ObjectId metaId;
       try (Repository repo = repoManager.openRepository(project)) {
-        Ref ref = repo.exactRef(RefNames.changeMetaRef(id));
+        Ref ref = repo.exactRef(RefNames.changeMetaRef(changeId));
         assertThat(ref).isNotNull();
         metaId = ref.getObjectId();
       }
 
-      ReviewDb db = ReviewDbUtil.unwrapDb(ctx.getReviewDbProvider().get());
-      Change c = db.changes().get(id);
-      assertThat(c).isNotNull();
-      NoteDbChangeState state = NoteDbChangeState.parse(c);
-      assertThat(state).isNotNull();
-      assertThat(state.getPrimaryStorage()).isEqualTo(PrimaryStorage.REVIEW_DB);
-      assertThat(state.getRefState()).hasValue(RefState.create(metaId, ImmutableMap.of()));
+      try (ReviewDb db = openUnderlyingReviewDb(ctx)) {
+        Change c = db.changes().get(changeId);
+        assertThat(c).isNotNull();
+        NoteDbChangeState state = NoteDbChangeState.parse(c);
+        assertThat(state).isNotNull();
+        assertThat(state.getPrimaryStorage()).isEqualTo(PrimaryStorage.REVIEW_DB);
+        assertThat(state.getRefState()).hasValue(RefState.create(metaId, ImmutableMap.of()));
+      }
     }
   }
 
-  private GerritServer startServer() throws Exception {
-    return GerritServer.start(serverDesc, new Config(), site);
+  @Test
+  public void migrateOneChange() throws Exception {
+    assertNotesMigrationState(NotesMigrationState.REVIEW_DB);
+    setUpOneChange();
+
+    migrate("--trial", "false");
+    assertNotesMigrationState(NotesMigrationState.NOTE_DB_UNFUSED);
+
+    try (ServerContext ctx = startServer()) {
+      GitRepositoryManager repoManager = ctx.getInjector().getInstance(GitRepositoryManager.class);
+      try (Repository repo = repoManager.openRepository(project)) {
+        assertThat(repo.exactRef(RefNames.changeMetaRef(changeId))).isNotNull();
+      }
+
+      try (ReviewDb db = openUnderlyingReviewDb(ctx)) {
+        Change c = db.changes().get(changeId);
+        assertThat(c).isNotNull();
+        NoteDbChangeState state = NoteDbChangeState.parse(c);
+        assertThat(state).isNotNull();
+        assertThat(state.getPrimaryStorage()).isEqualTo(PrimaryStorage.NOTE_DB);
+        assertThat(state.getRefState()).isEmpty();
+
+        ChangeInput in = new ChangeInput(project.get(), "master", "NoteDb-only change");
+        in.newBranch = true;
+        GerritApi gApi = ctx.getInjector().getInstance(GerritApi.class);
+        Change.Id id2 = new Change.Id(gApi.changes().create(in).info()._number);
+        assertThat(db.changes().get(id2)).isNull();
+      }
+    }
   }
 
-  private ManualRequestContext openContext(GerritServer server) throws Exception {
-    Injector i = server.getTestInjector();
-    TestAccount a = i.getInstance(AccountCreator.class).admin();
-    return openContext(server, a.getId());
+  @Test
+  public void migrationDoesNotRequireIndex() throws Exception {
+    assertNotesMigrationState(NotesMigrationState.REVIEW_DB);
+    setUpOneChange();
+
+    int version = ChangeSchemaDefinitions.INSTANCE.getLatest().getVersion();
+    GerritIndexStatus status = new GerritIndexStatus(sitePaths);
+    assertThat(status.getReady(ChangeSchemaDefinitions.NAME, version)).isTrue();
+    status.setReady(ChangeSchemaDefinitions.NAME, version, false);
+    status.save();
+
+    migrate("--trial", "false");
+    assertNotesMigrationState(NotesMigrationState.NOTE_DB_UNFUSED);
+
+    status = new GerritIndexStatus(sitePaths);
+    assertThat(status.getReady(ChangeSchemaDefinitions.NAME, version)).isFalse();
+
+    // TODO(dborowitz): Remove when offline migration includes reindex.
+    assertServerStartupFails();
   }
 
-  private ManualRequestContext openContext(GerritServer server, Account.Id accountId)
-      throws Exception {
-    return server.getTestInjector().getInstance(OneOffRequestContext.class).openAs(accountId);
+  private void setUpOneChange() throws Exception {
+    project = new Project.NameKey("project");
+    try (ServerContext ctx = startServer()) {
+      GerritApi gApi = ctx.getInjector().getInstance(GerritApi.class);
+      gApi.projects().create("project");
+
+      ChangeInput in = new ChangeInput(project.get(), "master", "Test change");
+      in.newBranch = true;
+      changeId = new Change.Id(gApi.changes().create(in).info()._number);
+    }
   }
 
   private void migrate(String... additionalArgs) throws Exception {
-    String[] args =
-        Stream.concat(
-                Stream.of("migrate-to-note-db", "-d", site.toString(), "--show-stack-trace"),
-                Stream.of(additionalArgs))
-            .toArray(String[]::new);
-    assertThat(GerritLauncher.mainImpl(args)).isEqualTo(0);
-  }
-
-  private void setNotesMigrationState(NotesMigrationState state) throws Exception {
-    gerritConfig.load();
-    ConfigNotesMigration.setConfigValues(gerritConfig, state.migration());
-    gerritConfig.save();
+    runGerrit(
+        ImmutableList.of(
+            "migrate-to-note-db", "-d", sitePaths.site_path.toString(), "--show-stack-trace"),
+        ImmutableList.copyOf(additionalArgs));
   }
 
   private void assertNotesMigrationState(NotesMigrationState expected) throws Exception {
@@ -187,4 +171,10 @@
     assertThat(NotesMigrationState.forNotesMigration(new ConfigNotesMigration(gerritConfig)))
         .hasValue(expected);
   }
+
+  private ReviewDb openUnderlyingReviewDb(ServerContext ctx) throws Exception {
+    return ctx.getInjector()
+        .getInstance(Key.get(new TypeLiteral<SchemaFactory<ReviewDb>>() {}, ReviewDbFactory.class))
+        .open();
+  }
 }
diff --git a/gerrit-acceptance-tests/src/test/java/com/google/gerrit/acceptance/pgm/ReindexIT.java b/gerrit-acceptance-tests/src/test/java/com/google/gerrit/acceptance/pgm/ReindexIT.java
index 79bbba2..10c51df 100644
--- a/gerrit-acceptance-tests/src/test/java/com/google/gerrit/acceptance/pgm/ReindexIT.java
+++ b/gerrit-acceptance-tests/src/test/java/com/google/gerrit/acceptance/pgm/ReindexIT.java
@@ -14,48 +14,14 @@
 
 package com.google.gerrit.acceptance.pgm;
 
-import static com.google.common.truth.Truth.assertThat;
-
-import com.google.gerrit.launcher.GerritLauncher;
-import com.google.gerrit.testutil.TempFileUtil;
-import java.io.File;
-import org.junit.After;
-import org.junit.Before;
+import com.google.gerrit.acceptance.NoHttpd;
+import com.google.gerrit.acceptance.StandaloneSiteTest;
 import org.junit.Test;
 
-public class ReindexIT {
-  private File sitePath;
-
-  @Before
-  public void createTempDirectory() throws Exception {
-    sitePath = TempFileUtil.createTempDirectory();
-  }
-
-  @After
-  public void destroySite() throws Exception {
-    if (sitePath != null) {
-      TempFileUtil.cleanup();
-    }
-  }
-
+@NoHttpd
+public class ReindexIT extends StandaloneSiteTest {
   @Test
   public void reindexEmptySite() throws Exception {
-    initSite();
-    runGerrit("reindex", "-d", sitePath.toString(), "--show-stack-trace");
-  }
-
-  private void initSite() throws Exception {
-    runGerrit(
-        "init",
-        "-d",
-        sitePath.getPath(),
-        "--batch",
-        "--no-auto-start",
-        "--skip-plugins",
-        "--show-stack-trace");
-  }
-
-  private static void runGerrit(String... args) throws Exception {
-    assertThat(GerritLauncher.mainImpl(args)).isEqualTo(0);
+    runGerrit("reindex", "-d", sitePaths.site_path.toString(), "--show-stack-trace");
   }
 }
diff --git a/gerrit-acceptance-tests/src/test/java/com/google/gerrit/acceptance/server/notedb/ChangeRebuilderIT.java b/gerrit-acceptance-tests/src/test/java/com/google/gerrit/acceptance/server/notedb/ChangeRebuilderIT.java
index c7840e7..1c55f76 100644
--- a/gerrit-acceptance-tests/src/test/java/com/google/gerrit/acceptance/server/notedb/ChangeRebuilderIT.java
+++ b/gerrit-acceptance-tests/src/test/java/com/google/gerrit/acceptance/server/notedb/ChangeRebuilderIT.java
@@ -122,6 +122,10 @@
     // want precise control over when auto-rebuilding happens.
     cfg.setBoolean("index", null, "testAutoReindexIfStale", false);
 
+    // setNotesMigration tries to keep IDs in sync between ReviewDb and NoteDb, which is behavior
+    // unique to this test. This gets prohibitively slow if we use the default sequence gap.
+    cfg.setInt("noteDb", "changes", "initialSequenceGap", 0);
+
     return cfg;
   }
 
diff --git a/gerrit-acceptance-tests/src/test/java/com/google/gerrit/acceptance/server/notedb/OnlineNoteDbMigrationIT.java b/gerrit-acceptance-tests/src/test/java/com/google/gerrit/acceptance/server/notedb/OnlineNoteDbMigrationIT.java
index 4008634..bb72a58 100644
--- a/gerrit-acceptance-tests/src/test/java/com/google/gerrit/acceptance/server/notedb/OnlineNoteDbMigrationIT.java
+++ b/gerrit-acceptance-tests/src/test/java/com/google/gerrit/acceptance/server/notedb/OnlineNoteDbMigrationIT.java
@@ -17,10 +17,18 @@
 import static com.google.common.truth.Truth.assertThat;
 import static com.google.common.truth.Truth8.assertThat;
 import static com.google.common.truth.TruthJUnit.assume;
+import static com.google.gerrit.server.notedb.NotesMigrationState.NOTE_DB_UNFUSED;
+import static com.google.gerrit.server.notedb.NotesMigrationState.READ_WRITE_NO_SEQUENCE;
+import static com.google.gerrit.server.notedb.NotesMigrationState.READ_WRITE_WITH_SEQUENCE_NOTE_DB_PRIMARY;
+import static com.google.gerrit.server.notedb.NotesMigrationState.READ_WRITE_WITH_SEQUENCE_REVIEW_DB_PRIMARY;
+import static com.google.gerrit.server.notedb.NotesMigrationState.REVIEW_DB;
+import static com.google.gerrit.server.notedb.NotesMigrationState.WRITE;
+import static java.nio.charset.StandardCharsets.UTF_8;
 
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
 import com.google.gerrit.acceptance.AbstractDaemonTest;
+import com.google.gerrit.acceptance.GerritConfig;
 import com.google.gerrit.acceptance.NoHttpd;
 import com.google.gerrit.acceptance.PushOneCommit;
 import com.google.gerrit.acceptance.Sandboxed;
@@ -28,6 +36,7 @@
 import com.google.gerrit.reviewdb.client.Project;
 import com.google.gerrit.reviewdb.client.RefNames;
 import com.google.gerrit.reviewdb.server.ReviewDb;
+import com.google.gerrit.server.Sequences;
 import com.google.gerrit.server.config.SitePaths;
 import com.google.gerrit.server.notedb.ConfigNotesMigration;
 import com.google.gerrit.server.notedb.NoteDbChangeState;
@@ -37,13 +46,18 @@
 import com.google.gerrit.server.notedb.rebuild.MigrationException;
 import com.google.gerrit.server.notedb.rebuild.NoteDbMigrator;
 import com.google.gerrit.server.schema.ReviewDbFactory;
+import com.google.gerrit.testutil.ConfigSuite;
 import com.google.gerrit.testutil.NoteDbMode;
 import com.google.gwtorm.server.SchemaFactory;
 import com.google.inject.Inject;
 import com.google.inject.Provider;
 import java.util.List;
 import org.eclipse.jgit.junit.TestRepository;
+import org.eclipse.jgit.lib.Config;
+import org.eclipse.jgit.lib.Constants;
 import org.eclipse.jgit.lib.ObjectId;
+import org.eclipse.jgit.lib.ObjectLoader;
+import org.eclipse.jgit.lib.ObjectReader;
 import org.eclipse.jgit.lib.Ref;
 import org.eclipse.jgit.lib.Repository;
 import org.eclipse.jgit.storage.file.FileBasedConfig;
@@ -56,12 +70,21 @@
 public class OnlineNoteDbMigrationIT extends AbstractDaemonTest {
   private static final String INVALID_STATE = "deadbeefdeadbeefdeadbeefdeadbeefdeadbeef";
 
+  @ConfigSuite.Default
+  public static Config defaultConfig() {
+    Config cfg = new Config();
+    cfg.setInt("noteDb", "changes", "sequenceBatchSize", 10);
+    cfg.setInt("noteDb", "changes", "initialSequenceGap", 500);
+    return cfg;
+  }
+
   // Tests in this class are generally interested in the actual ReviewDb contents, but the shifting
   // migration state may result in various kinds of wrappers showing up unexpectedly.
   @Inject @ReviewDbFactory private SchemaFactory<ReviewDb> schemaFactory;
 
   @Inject private SitePaths sitePaths;
   @Inject private Provider<NoteDbMigrator.Builder> migratorBuilderProvider;
+  @Inject private Sequences sequences;
 
   private FileBasedConfig gerritConfig;
 
@@ -69,7 +92,7 @@
   public void setUp() throws Exception {
     assume().that(NoteDbMode.get()).isEqualTo(NoteDbMode.OFF);
     gerritConfig = new FileBasedConfig(sitePaths.gerrit_config.toFile(), FS.detect());
-    assertNotesMigrationState(NotesMigrationState.REVIEW_DB);
+    assertNotesMigrationState(REVIEW_DB);
   }
 
   @Test
@@ -89,13 +112,13 @@
         b -> b.setProjects(ps),
         NoteDbMigrator::migrate);
 
-    setNotesMigrationState(NotesMigrationState.READ_WRITE_WITH_SEQUENCE_REVIEW_DB_PRIMARY);
+    setNotesMigrationState(READ_WRITE_WITH_SEQUENCE_REVIEW_DB_PRIMARY);
     assertMigrationException(
         "Migration has already progressed past the endpoint of the \"trial mode\" state",
         b -> b.setTrialMode(true),
         NoteDbMigrator::migrate);
 
-    setNotesMigrationState(NotesMigrationState.READ_WRITE_WITH_SEQUENCE_NOTE_DB_PRIMARY);
+    setNotesMigrationState(READ_WRITE_WITH_SEQUENCE_NOTE_DB_PRIMARY);
     assertMigrationException(
         "Cannot force rebuild changes; NoteDb is already the primary storage for some changes",
         b -> b.setForceRebuild(true),
@@ -103,6 +126,13 @@
   }
 
   @Test
+  @GerritConfig(name = "noteDb.changes.initialSequenceGap", value = "-7")
+  public void initialSequenceGapMustBeNonNegative() throws Exception {
+    setNotesMigrationState(READ_WRITE_NO_SEQUENCE);
+    assertMigrationException("Sequence gap must be non-negative: -7", b -> b, m -> {});
+  }
+
+  @Test
   public void rebuildOneChangeTrialModeAndForceRebuild() throws Exception {
     PushOneCommit.Result r = createChange();
     Change.Id id = r.getChange().getId();
@@ -110,7 +140,7 @@
     try (NoteDbMigrator migrator = migratorBuilderProvider.get().setTrialMode(true).build()) {
       migrator.migrate();
     }
-    assertNotesMigrationState(NotesMigrationState.READ_WRITE_NO_SEQUENCE);
+    assertNotesMigrationState(READ_WRITE_NO_SEQUENCE);
 
     ObjectId oldMetaId;
     try (Repository repo = repoManager.openRepository(project);
@@ -134,7 +164,7 @@
     }
 
     migrate(b -> b.setTrialMode(true));
-    assertNotesMigrationState(NotesMigrationState.READ_WRITE_NO_SEQUENCE);
+    assertNotesMigrationState(READ_WRITE_NO_SEQUENCE);
 
     try (Repository repo = repoManager.openRepository(project);
         ReviewDb db = schemaFactory.open()) {
@@ -145,7 +175,7 @@
     }
 
     migrate(b -> b.setTrialMode(true).setForceRebuild(true));
-    assertNotesMigrationState(NotesMigrationState.READ_WRITE_NO_SEQUENCE);
+    assertNotesMigrationState(READ_WRITE_NO_SEQUENCE);
 
     try (Repository repo = repoManager.openRepository(project);
         ReviewDb db = schemaFactory.open()) {
@@ -163,7 +193,7 @@
 
   @Test
   public void rebuildSubsetOfChanges() throws Exception {
-    setNotesMigrationState(NotesMigrationState.WRITE);
+    setNotesMigrationState(WRITE);
 
     PushOneCommit.Result r1 = createChange();
     PushOneCommit.Result r2 = createChange();
@@ -191,7 +221,7 @@
 
   @Test
   public void rebuildSubsetOfProjects() throws Exception {
-    setNotesMigrationState(NotesMigrationState.WRITE);
+    setNotesMigrationState(WRITE);
 
     Project.NameKey p2 = createProject("project2");
     TestRepository<?> tr2 = cloneProject(p2, admin);
@@ -221,6 +251,92 @@
     }
   }
 
+  @Test
+  public void enableSequencesNoGap() throws Exception {
+    testEnableSequences(0, 2, "12");
+  }
+
+  @Test
+  public void enableSequencesWithGap() throws Exception {
+    testEnableSequences(-1, 502, "512");
+  }
+
+  private void testEnableSequences(int builderOption, int expectedFirstId, String expectedRefValue)
+      throws Exception {
+    PushOneCommit.Result r = createChange();
+    Change.Id id = r.getChange().getId();
+    assertThat(id.get()).isEqualTo(1);
+
+    migrate(
+        b ->
+            b.setSequenceGap(builderOption)
+                .setStopAtStateForTesting(READ_WRITE_WITH_SEQUENCE_REVIEW_DB_PRIMARY));
+
+    assertThat(sequences.nextChangeId()).isEqualTo(expectedFirstId);
+    assertThat(sequences.nextChangeId()).isEqualTo(expectedFirstId + 1);
+
+    try (Repository repo = repoManager.openRepository(allProjects);
+        ObjectReader reader = repo.newObjectReader()) {
+      Ref ref = repo.exactRef("refs/sequences/changes");
+      assertThat(ref).isNotNull();
+      ObjectLoader loader = reader.open(ref.getObjectId());
+      assertThat(loader.getType()).isEqualTo(Constants.OBJ_BLOB);
+      // Acquired a block of 10 to serve the first nextChangeId call after migration.
+      assertThat(new String(loader.getCachedBytes(), UTF_8)).isEqualTo(expectedRefValue);
+    }
+
+    try (ReviewDb db = schemaFactory.open()) {
+      // Underlying, unused ReviewDb is still on its own sequence.
+      @SuppressWarnings("deprecation")
+      int nextFromReviewDb = db.nextChangeId();
+      assertThat(nextFromReviewDb).isEqualTo(3);
+    }
+  }
+
+  @Test
+  public void fullMigration() throws Exception {
+    PushOneCommit.Result r = createChange();
+    Change.Id id = r.getChange().getId();
+
+    migrate(b -> b);
+    assertNotesMigrationState(NOTE_DB_UNFUSED);
+
+    assertThat(sequences.nextChangeId()).isEqualTo(502);
+
+    ObjectId oldMetaId;
+    int rowVersion;
+    try (ReviewDb db = schemaFactory.open();
+        Repository repo = repoManager.openRepository(project)) {
+      Ref ref = repo.exactRef(RefNames.changeMetaRef(id));
+      assertThat(ref).isNotNull();
+      oldMetaId = ref.getObjectId();
+
+      Change c = db.changes().get(id);
+      assertThat(c.getTopic()).isNull();
+      rowVersion = c.getRowVersion();
+      NoteDbChangeState s = NoteDbChangeState.parse(c);
+      assertThat(s.getPrimaryStorage()).isEqualTo(PrimaryStorage.NOTE_DB);
+      assertThat(s.getRefState()).isEmpty();
+    }
+
+    // Do not open a new context, to simulate races with other threads that opened a context earlier
+    // in the migration process; this needs to work.
+    gApi.changes().id(id.get()).topic(name("a-topic"));
+
+    // Of course, it should also work with a new context.
+    resetCurrentApiUser();
+    gApi.changes().id(id.get()).topic(name("another-topic"));
+
+    try (ReviewDb db = schemaFactory.open();
+        Repository repo = repoManager.openRepository(project)) {
+      assertThat(repo.exactRef(RefNames.changeMetaRef(id)).getObjectId()).isNotEqualTo(oldMetaId);
+
+      Change c = db.changes().get(id);
+      assertThat(c.getTopic()).isNull();
+      assertThat(c.getRowVersion()).isEqualTo(rowVersion);
+    }
+  }
+
   private void assertNotesMigrationState(NotesMigrationState expected) throws Exception {
     assertThat(NotesMigrationState.forNotesMigration(notesMigration)).hasValue(expected);
     gerritConfig.load();
diff --git a/gerrit-pgm/src/main/java/com/google/gerrit/pgm/MigrateToNoteDb.java b/gerrit-pgm/src/main/java/com/google/gerrit/pgm/MigrateToNoteDb.java
index 9a1cc49..3cbf71a 100644
--- a/gerrit-pgm/src/main/java/com/google/gerrit/pgm/MigrateToNoteDb.java
+++ b/gerrit-pgm/src/main/java/com/google/gerrit/pgm/MigrateToNoteDb.java
@@ -37,6 +37,7 @@
 import java.util.ArrayList;
 import java.util.List;
 import org.kohsuke.args4j.Option;
+import org.kohsuke.args4j.spi.ExplicitBooleanOptionHandler;
 
 public class MigrateToNoteDb extends SiteProgram {
   @Option(name = "--threads", usage = "Number of threads to use for rebuilding NoteDb")
@@ -70,10 +71,20 @@
     name = "--trial",
     usage =
         "trial mode: migrate changes and turn on reading from NoteDb, but leave ReviewDb as"
-            + " the source of truth"
+            + " the source of truth",
+    handler = ExplicitBooleanOptionHandler.class
   )
   private boolean trial = true; // TODO(dborowitz): Default to false in 3.0.
 
+  @Option(
+    name = "--sequence-gap",
+    usage =
+        "gap in change sequence numbers between last ReviewDb number and first NoteDb number;"
+            + " negative indicates using the value of noteDb.changes.initialSequenceGap (default"
+            + " 1000)"
+  )
+  private int sequenceGap;
+
   private Injector dbInjector;
   private Injector sysInjector;
   private LifecycleManager dbManager;
@@ -108,6 +119,7 @@
               .setChanges(changes.stream().map(Change.Id::new).collect(toList()))
               .setTrialMode(trial)
               .setForceRebuild(force)
+              .setSequenceGap(sequenceGap)
               .build()) {
         if (!projects.isEmpty() || !changes.isEmpty()) {
           migrator.rebuild();
diff --git a/gerrit-server/src/main/java/com/google/gerrit/server/Sequences.java b/gerrit-server/src/main/java/com/google/gerrit/server/Sequences.java
index e6d56ee..f1f0e6f 100644
--- a/gerrit-server/src/main/java/com/google/gerrit/server/Sequences.java
+++ b/gerrit-server/src/main/java/com/google/gerrit/server/Sequences.java
@@ -37,6 +37,10 @@
 public class Sequences {
   public static final String CHANGES = "changes";
 
+  public static int getChangeSequenceGap(Config cfg) {
+    return cfg.getInt("noteDb", "changes", "initialSequenceGap", 1000);
+  }
+
   private final Provider<ReviewDb> db;
   private final NotesMigration migration;
   private final RepoSequence changeSeq;
@@ -51,7 +55,7 @@
     this.db = db;
     this.migration = migration;
 
-    int gap = cfg.getInt("noteDb", "changes", "initialSequenceGap", 0);
+    int gap = getChangeSequenceGap(cfg);
     changeSeq =
         new RepoSequence(
             repoManager,
diff --git a/gerrit-server/src/main/java/com/google/gerrit/server/notedb/rebuild/NoteDbMigrator.java b/gerrit-server/src/main/java/com/google/gerrit/server/notedb/rebuild/NoteDbMigrator.java
index a40f9cf..a866314 100644
--- a/gerrit-server/src/main/java/com/google/gerrit/server/notedb/rebuild/NoteDbMigrator.java
+++ b/gerrit-server/src/main/java/com/google/gerrit/server/notedb/rebuild/NoteDbMigrator.java
@@ -16,19 +16,21 @@
 
 import static com.google.common.base.Preconditions.checkArgument;
 import static com.google.common.base.Preconditions.checkNotNull;
+import static com.google.common.base.Preconditions.checkState;
 import static com.google.gerrit.reviewdb.server.ReviewDbUtil.unwrapDb;
 import static com.google.gerrit.server.notedb.NotesMigrationState.NOTE_DB_UNFUSED;
 import static com.google.gerrit.server.notedb.NotesMigrationState.READ_WRITE_NO_SEQUENCE;
+import static com.google.gerrit.server.notedb.NotesMigrationState.READ_WRITE_WITH_SEQUENCE_NOTE_DB_PRIMARY;
 import static com.google.gerrit.server.notedb.NotesMigrationState.READ_WRITE_WITH_SEQUENCE_REVIEW_DB_PRIMARY;
 import static com.google.gerrit.server.notedb.NotesMigrationState.WRITE;
 import static java.nio.charset.StandardCharsets.UTF_8;
 import static java.util.Comparator.comparing;
+import static java.util.stream.Collectors.toList;
 
-import com.google.common.base.Predicates;
+import com.google.common.annotations.VisibleForTesting;
 import com.google.common.base.Stopwatch;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableListMultimap;
-import com.google.common.collect.Iterables;
 import com.google.common.collect.MultimapBuilder;
 import com.google.common.collect.Ordering;
 import com.google.common.collect.SetMultimap;
@@ -42,12 +44,18 @@
 import com.google.gerrit.reviewdb.client.Change;
 import com.google.gerrit.reviewdb.client.Project;
 import com.google.gerrit.reviewdb.server.ReviewDb;
+import com.google.gerrit.server.Sequences;
+import com.google.gerrit.server.config.AllProjectsName;
+import com.google.gerrit.server.config.GerritServerConfig;
 import com.google.gerrit.server.config.SitePaths;
+import com.google.gerrit.server.git.GitRepositoryManager;
 import com.google.gerrit.server.git.LockFailureException;
 import com.google.gerrit.server.git.WorkQueue;
 import com.google.gerrit.server.notedb.ConfigNotesMigration;
 import com.google.gerrit.server.notedb.NotesMigration;
 import com.google.gerrit.server.notedb.NotesMigrationState;
+import com.google.gerrit.server.notedb.PrimaryStorageMigrator;
+import com.google.gerrit.server.notedb.RepoSequence;
 import com.google.gerrit.server.notedb.rebuild.ChangeRebuilder.NoPatchSetsException;
 import com.google.gwtorm.server.OrmException;
 import com.google.gwtorm.server.SchemaFactory;
@@ -65,6 +73,7 @@
 import java.util.concurrent.TimeUnit;
 import java.util.function.Predicate;
 import org.eclipse.jgit.errors.ConfigInvalidException;
+import org.eclipse.jgit.lib.Config;
 import org.eclipse.jgit.lib.ProgressMonitor;
 import org.eclipse.jgit.lib.TextProgressMonitor;
 import org.eclipse.jgit.storage.file.FileBasedConfig;
@@ -78,31 +87,45 @@
   private static final Logger log = LoggerFactory.getLogger(NoteDbMigrator.class);
 
   public static class Builder {
+    private final Config cfg;
     private final SitePaths sitePaths;
     private final SchemaFactory<ReviewDb> schemaFactory;
+    private final GitRepositoryManager repoManager;
+    private final AllProjectsName allProjects;
     private final ChangeRebuilder rebuilder;
     private final WorkQueue workQueue;
     private final NotesMigration globalNotesMigration;
+    private final PrimaryStorageMigrator primaryStorageMigrator;
 
     private int threads;
     private ImmutableList<Project.NameKey> projects = ImmutableList.of();
     private ImmutableList<Change.Id> changes = ImmutableList.of();
     private OutputStream progressOut = NullOutputStream.INSTANCE;
+    private NotesMigrationState stopAtState;
     private boolean trial;
     private boolean forceRebuild;
+    private int sequenceGap = -1;
 
     @Inject
     Builder(
+        @GerritServerConfig Config cfg,
         SitePaths sitePaths,
         SchemaFactory<ReviewDb> schemaFactory,
+        GitRepositoryManager repoManager,
+        AllProjectsName allProjects,
         ChangeRebuilder rebuilder,
         WorkQueue workQueue,
-        NotesMigration globalNotesMigration) {
+        NotesMigration globalNotesMigration,
+        PrimaryStorageMigrator primaryStorageMigrator) {
+      this.cfg = cfg;
       this.sitePaths = sitePaths;
       this.schemaFactory = schemaFactory;
+      this.repoManager = repoManager;
+      this.allProjects = allProjects;
       this.rebuilder = rebuilder;
       this.workQueue = workQueue;
       this.globalNotesMigration = globalNotesMigration;
+      this.primaryStorageMigrator = primaryStorageMigrator;
     }
 
     /**
@@ -166,6 +189,18 @@
     }
 
     /**
+     * Stop at a specific migration state, for testing only.
+     *
+     * @param stopAtState state to stop at.
+     * @return this.
+     */
+    @VisibleForTesting
+    public Builder setStopAtStateForTesting(NotesMigrationState stopAtState) {
+      this.stopAtState = stopAtState;
+      return this;
+    }
+
+    /**
      * Rebuild in "trial mode": configure Gerrit to write to and read from NoteDb, but leave
      * ReviewDb as the source of truth for all changes.
      *
@@ -196,61 +231,108 @@
       return this;
     }
 
+    /**
+     * Gap between ReviewDb change sequence numbers and NoteDb.
+     *
+     * <p>If NoteDb sequences are enabled in a running server, there is a race between the migration
+     * step that calls {@code nextChangeId()} to seed the ref, and other threads that call {@code
+     * nextChangeId()} to create new changes. In order to prevent these operations stepping on one
+     * another, we use this value to skip some predefined sequence numbers. This is strongly
+     * recommended in a running server.
+     *
+     * <p>If the migration takes place offline, there is no race with other threads, and this option
+     * may be set to 0. However, admins may still choose to use a gap, for example to make it easier
+     * to distinguish changes that were created before and after the NoteDb migration.
+     *
+     * <p>By default, uses the value from {@code noteDb.changes.initialSequenceGap} in {@code
+     * gerrit.config}, which defaults to 1000.
+     *
+     * @param sequenceGap sequence gap size; if negative, use the default.
+     * @return this.
+     */
+    public Builder setSequenceGap(int sequenceGap) {
+      this.sequenceGap = sequenceGap;
+      return this;
+    }
+
     public NoteDbMigrator build() throws MigrationException {
       return new NoteDbMigrator(
           sitePaths,
           schemaFactory,
+          repoManager,
+          allProjects,
           rebuilder,
           globalNotesMigration,
+          primaryStorageMigrator,
           threads > 1
               ? MoreExecutors.listeningDecorator(workQueue.createQueue(threads, "RebuildChange"))
               : MoreExecutors.newDirectExecutorService(),
           projects,
           changes,
           progressOut,
+          stopAtState,
           trial,
-          forceRebuild);
+          forceRebuild,
+          sequenceGap >= 0 ? sequenceGap : Sequences.getChangeSequenceGap(cfg));
     }
   }
 
   private final FileBasedConfig gerritConfig;
   private final SchemaFactory<ReviewDb> schemaFactory;
+  private final GitRepositoryManager repoManager;
+  private final AllProjectsName allProjects;
   private final ChangeRebuilder rebuilder;
   private final NotesMigration globalNotesMigration;
+  private final PrimaryStorageMigrator primaryStorageMigrator;
 
   private final ListeningExecutorService executor;
   private final ImmutableList<Project.NameKey> projects;
   private final ImmutableList<Change.Id> changes;
   private final OutputStream progressOut;
+  private final NotesMigrationState stopAtState;
   private final boolean trial;
   private final boolean forceRebuild;
+  private final int sequenceGap;
 
   private NoteDbMigrator(
       SitePaths sitePaths,
       SchemaFactory<ReviewDb> schemaFactory,
+      GitRepositoryManager repoManager,
+      AllProjectsName allProjects,
       ChangeRebuilder rebuilder,
       NotesMigration globalNotesMigration,
+      PrimaryStorageMigrator primaryStorageMigrator,
       ListeningExecutorService executor,
       ImmutableList<Project.NameKey> projects,
       ImmutableList<Change.Id> changes,
       OutputStream progressOut,
+      NotesMigrationState stopAtState,
       boolean trial,
-      boolean forceRebuild)
+      boolean forceRebuild,
+      int sequenceGap)
       throws MigrationException {
     if (!changes.isEmpty() && !projects.isEmpty()) {
       throw new MigrationException("Cannot set both changes and projects");
     }
+    if (sequenceGap < 0) {
+      throw new MigrationException("Sequence gap must be non-negative: " + sequenceGap);
+    }
 
     this.schemaFactory = schemaFactory;
     this.rebuilder = rebuilder;
+    this.repoManager = repoManager;
+    this.allProjects = allProjects;
     this.globalNotesMigration = globalNotesMigration;
+    this.primaryStorageMigrator = primaryStorageMigrator;
     this.gerritConfig = new FileBasedConfig(sitePaths.gerrit_config.toFile(), FS.detect());
     this.executor = executor;
     this.projects = projects;
     this.changes = changes;
     this.progressOut = progressOut;
+    this.stopAtState = stopAtState;
     this.trial = trial;
     this.forceRebuild = forceRebuild;
+    this.sequenceGap = sequenceGap;
   }
 
   @Override
@@ -281,6 +363,9 @@
 
     boolean rebuilt = false;
     while (state.compareTo(NOTE_DB_UNFUSED) < 0) {
+      if (state.equals(stopAtState)) {
+        return;
+      }
       boolean stillNeedsRebuild = forceRebuild && !rebuilt;
       if (trial && state.compareTo(READ_WRITE_NO_SEQUENCE) >= 0) {
         if (stillNeedsRebuild && state == READ_WRITE_NO_SEQUENCE) {
@@ -303,7 +388,7 @@
             state = rebuildAndEnableReads(state);
             rebuilt = true;
           } else {
-            state = enableSequences();
+            state = enableSequences(state);
           }
           break;
         case READ_WRITE_WITH_SEQUENCE_REVIEW_DB_PRIMARY:
@@ -311,11 +396,16 @@
             state = rebuildAndEnableReads(state);
             rebuilt = true;
           } else {
-            state = setNoteDbPrimary();
+            state = setNoteDbPrimary(state);
           }
           break;
         case READ_WRITE_WITH_SEQUENCE_NOTE_DB_PRIMARY:
-          state = disableReviewDb();
+          // The only way we can get here is if there was a failure on a previous run of
+          // setNoteDbPrimary, since that method moves to NOTE_DB_UNFUSED if it completes
+          // successfully. Assume that not all changes were converted and re-run the step.
+          // migrateToNoteDbPrimary is a relatively fast no-op for already-migrated changes, so this
+          // isn't actually repeating work.
+          state = setNoteDbPrimary(state);
           break;
         case NOTE_DB_UNFUSED:
           // Done!
@@ -340,16 +430,80 @@
     return saveState(prev, READ_WRITE_NO_SEQUENCE);
   }
 
-  private NotesMigrationState enableSequences() {
-    throw new UnsupportedOperationException("not yet implemented");
+  private NotesMigrationState enableSequences(NotesMigrationState prev)
+      throws OrmException, IOException {
+    try (ReviewDb db = schemaFactory.open()) {
+      @SuppressWarnings("deprecation")
+      RepoSequence seq =
+          new RepoSequence(
+              repoManager,
+              allProjects,
+              Sequences.CHANGES,
+              // If sequenceGap is 0, this writes into the sequence ref the same ID that is returned
+              // by the call to seq.next() below. If we actually used this as a change ID, that
+              // would be a problem, but we just discard it, so this is safe.
+              () -> db.nextChangeId() + sequenceGap - 1,
+              1);
+      seq.next();
+    }
+    return saveState(prev, READ_WRITE_WITH_SEQUENCE_REVIEW_DB_PRIMARY);
   }
 
-  private NotesMigrationState setNoteDbPrimary() {
-    throw new UnsupportedOperationException("not yet implemented");
+  private NotesMigrationState setNoteDbPrimary(NotesMigrationState prev)
+      throws MigrationException, OrmException, IOException {
+    checkState(
+        projects.isEmpty() && changes.isEmpty(),
+        "Should not have attempted setNoteDbPrimary with a subset of changes");
+    checkState(
+        prev == READ_WRITE_WITH_SEQUENCE_REVIEW_DB_PRIMARY
+            || prev == READ_WRITE_WITH_SEQUENCE_NOTE_DB_PRIMARY,
+        "Unexpected start state for setNoteDbPrimary: %s",
+        prev);
+
+    // Before changing the primary storage of old changes, ensure new changes are created with
+    // NoteDb primary.
+    prev = saveState(prev, READ_WRITE_WITH_SEQUENCE_NOTE_DB_PRIMARY);
+
+    Stopwatch sw = Stopwatch.createStarted();
+    log.info("Setting primary storage to NoteDb");
+    List<Change.Id> allChanges;
+    try (ReviewDb db = unwrapDb(schemaFactory.open())) {
+      allChanges = Streams.stream(db.changes().all()).map(Change::getId).collect(toList());
+    }
+
+    List<ListenableFuture<Boolean>> futures =
+        allChanges
+            .stream()
+            .map(
+                id ->
+                    executor.submit(
+                        () -> {
+                          // TODO(dborowitz): Avoid reopening db if using a single thread.
+                          try (ReviewDb db = unwrapDb(schemaFactory.open())) {
+                            primaryStorageMigrator.migrateToNoteDbPrimary(id);
+                            return true;
+                          } catch (Exception e) {
+                            log.error("Error migrating primary storage for " + id, e);
+                            return false;
+                          }
+                        }))
+            .collect(toList());
+
+    boolean ok = futuresToBoolean(futures, "Error migrating primary storage");
+    double t = sw.elapsed(TimeUnit.MILLISECONDS) / 1000d;
+    log.info(
+        String.format(
+            "Migrated primary storage of %d changes in %.01fs (%.01f/s)\n",
+            allChanges.size(), t, allChanges.size() / t));
+    if (!ok) {
+      throw new MigrationException("Migrating primary storage for some changes failed, see log");
+    }
+
+    return disableReviewDb(prev);
   }
 
-  private NotesMigrationState disableReviewDb() {
-    throw new UnsupportedOperationException("not yet implemented");
+  private NotesMigrationState disableReviewDb(NotesMigrationState prev) throws IOException {
+    return saveState(prev, NOTE_DB_UNFUSED);
   }
 
   private Optional<NotesMigrationState> loadState() throws IOException {
@@ -394,7 +548,6 @@
     if (!globalNotesMigration.commitChangeWrites()) {
       throw new MigrationException("Cannot rebuild without noteDb.changes.write=true");
     }
-    boolean ok;
     Stopwatch sw = Stopwatch.createStarted();
     log.info("Rebuilding changes in NoteDb");
 
@@ -416,13 +569,7 @@
       futures.add(future);
     }
 
-    try {
-      ok = Iterables.all(Futures.allAsList(futures).get(), Predicates.equalTo(true));
-    } catch (InterruptedException | ExecutionException e) {
-      log.error("Error rebuilding projects", e);
-      ok = false;
-    }
-
+    boolean ok = futuresToBoolean(futures, "Error rebuilding projects");
     double t = sw.elapsed(TimeUnit.MILLISECONDS) / 1000d;
     log.info(
         String.format(
@@ -502,4 +649,13 @@
     }
     return ok;
   }
+
+  private static boolean futuresToBoolean(List<ListenableFuture<Boolean>> futures, String errMsg) {
+    try {
+      return Futures.allAsList(futures).get().stream().allMatch(b -> b);
+    } catch (InterruptedException | ExecutionException e) {
+      log.error(errMsg, e);
+      return false;
+    }
+  }
 }
diff --git a/gerrit-server/src/main/java/com/google/gerrit/server/update/FusedNoteDbBatchUpdate.java b/gerrit-server/src/main/java/com/google/gerrit/server/update/FusedNoteDbBatchUpdate.java
index b979636..7db5e43 100644
--- a/gerrit-server/src/main/java/com/google/gerrit/server/update/FusedNoteDbBatchUpdate.java
+++ b/gerrit-server/src/main/java/com/google/gerrit/server/update/FusedNoteDbBatchUpdate.java
@@ -286,7 +286,6 @@
       @Assisted CurrentUser user,
       @Assisted Timestamp when) {
     super(repoManager, serverIdent, project, user, when);
-    checkArgument(!db.changesTablesEnabled(), "expected Change tables to be disabled on %s", db);
     this.changeNotesFactory = changeNotesFactory;
     this.changeControlFactory = changeControlFactory;
     this.changeUpdateFactory = changeUpdateFactory;
diff --git a/gerrit-server/src/main/java/com/google/gerrit/server/update/UnfusedNoteDbBatchUpdate.java b/gerrit-server/src/main/java/com/google/gerrit/server/update/UnfusedNoteDbBatchUpdate.java
index b5c7256..ce96c0e 100644
--- a/gerrit-server/src/main/java/com/google/gerrit/server/update/UnfusedNoteDbBatchUpdate.java
+++ b/gerrit-server/src/main/java/com/google/gerrit/server/update/UnfusedNoteDbBatchUpdate.java
@@ -14,7 +14,6 @@
 
 package com.google.gerrit.server.update;
 
-import static com.google.common.base.Preconditions.checkArgument;
 import static com.google.common.base.Preconditions.checkNotNull;
 import static java.util.Comparator.comparing;
 import static java.util.stream.Collectors.toList;
@@ -267,7 +266,6 @@
       @Assisted CurrentUser user,
       @Assisted Timestamp when) {
     super(repoManager, serverIdent, project, user, when);
-    checkArgument(!db.changesTablesEnabled(), "expected Change tables to be disabled on %s", db);
     this.changeNotesFactory = changeNotesFactory;
     this.changeControlFactory = changeControlFactory;
     this.changeUpdateFactory = changeUpdateFactory;
diff --git a/gerrit-server/src/test/java/com/google/gerrit/server/notedb/RepoSequenceTest.java b/gerrit-server/src/test/java/com/google/gerrit/server/notedb/RepoSequenceTest.java
index 4b302b7..66ccdad 100644
--- a/gerrit-server/src/test/java/com/google/gerrit/server/notedb/RepoSequenceTest.java
+++ b/gerrit-server/src/test/java/com/google/gerrit/server/notedb/RepoSequenceTest.java
@@ -264,13 +264,7 @@
       Runnable afterReadRef,
       Retryer<RefUpdate.Result> retryer) {
     return new RepoSequence(
-        repoManager,
-        project,
-        name,
-        () -> start,
-        batchSize,
-        afterReadRef,
-        retryer);
+        repoManager, project, name, () -> start, batchSize, afterReadRef, retryer);
   }
 
   private ObjectId writeBlob(String sequenceName, String value) {