diff --git a/ddl/backfilling.go b/ddl/backfilling.go
index 0c06fa0fab551..76e1fc2aaf5fd 100644
--- a/ddl/backfilling.go
+++ b/ddl/backfilling.go
@@ -725,7 +725,7 @@ func (b *backfillScheduler) adjustWorkerSize() error {
 	if b.copReqSenderPool != nil {
 		b.copReqSenderPool.adjustSize(len(b.workers))
 	}
-	return injectCheckBackfillWorkerNum(len(b.workers))
+	return injectCheckBackfillWorkerNum(len(b.workers), b.tp == typeAddIndexMergeTmpWorker)
 }
 
 func (b *backfillScheduler) initCopReqSenderPool() {
@@ -871,7 +871,10 @@ func (dc *ddlCtx) writePhysicalTableRecord(sessPool *sessionPool, t table.Physic
 	return nil
 }
 
-func injectCheckBackfillWorkerNum(curWorkerSize int) error {
+func injectCheckBackfillWorkerNum(curWorkerSize int, isMergeWorker bool) error {
+	if isMergeWorker {
+		return nil
+	}
 	failpoint.Inject("checkBackfillWorkerNum", func(val failpoint.Value) {
 		//nolint:forcetypeassert
 		if val.(bool) {
diff --git a/ddl/cancel_test.go b/ddl/cancel_test.go
index 431b97357b2db..cd446f3441baf 100644
--- a/ddl/cancel_test.go
+++ b/ddl/cancel_test.go
@@ -232,8 +232,6 @@ func TestCancel(t *testing.T) {
 
 	// Prepare schema.
 	tk.MustExec("use test")
-	// TODO: Will check why tidb_ddl_enable_fast_reorg could not default be on in another PR.
-	tk.MustExec("set global tidb_ddl_enable_fast_reorg = 0;")
 	tk.MustExec("drop table if exists t_partition;")
 	tk.MustExec(`create table t_partition (
 		c1 int, c2 int, c3 int
diff --git a/ddl/db_change_test.go b/ddl/db_change_test.go
index ee0634215c465..6de1376e2b75b 100644
--- a/ddl/db_change_test.go
+++ b/ddl/db_change_test.go
@@ -1719,7 +1719,7 @@ func TestCreateUniqueExpressionIndex(t *testing.T) {
 
 	tk := testkit.NewTestKit(t, store)
 	tk.MustExec("use test")
-	// TODO: will check why tidb_ddl_enable_fast_reorg could not default be on in another pr.pr.
+	// TODO: Will check why tidb_ddl_enable_fast_reorg could not default be on in another PR.
 	tk.MustExec("set global tidb_ddl_enable_fast_reorg = 0;")
 	tk.MustExec("create table t(a int default 0, b int default 0)")
 	tk.MustExec("insert into t values (1, 1), (2, 2), (3, 3), (4, 4)")
diff --git a/ddl/failtest/fail_db_test.go b/ddl/failtest/fail_db_test.go
index ece5b804ae336..d12c2182f9730 100644
--- a/ddl/failtest/fail_db_test.go
+++ b/ddl/failtest/fail_db_test.go
@@ -320,8 +320,6 @@ func TestRunDDLJobPanicEnableClusteredIndex(t *testing.T) {
 	s := createFailDBSuite(t)
 	testAddIndexWorkerNum(t, s, func(tk *testkit.TestKit) {
 		tk.Session().GetSessionVars().EnableClusteredIndex = variable.ClusteredIndexDefModeOn
-		// TODO: will check why tidb_ddl_enable_fast_reorg could not default be on in another pr.
-		tk.MustExec("set global tidb_ddl_enable_fast_reorg = 0;")
 		tk.MustExec("create table test_add_index (c1 bigint, c2 bigint, c3 bigint, primary key(c1, c3))")
 	})
 }
@@ -330,8 +328,6 @@ func TestRunDDLJobPanicEnableClusteredIndex(t *testing.T) {
 func TestRunDDLJobPanicDisableClusteredIndex(t *testing.T) {
 	s := createFailDBSuite(t)
 	testAddIndexWorkerNum(t, s, func(tk *testkit.TestKit) {
-		// TODO: will check why tidb_ddl_enable_fast_reorg could not default be on in another pr.
-		tk.MustExec("set global tidb_ddl_enable_fast_reorg = 0;")
 		tk.MustExec("create table test_add_index (c1 bigint, c2 bigint, c3 bigint, primary key(c1))")
 	})
 }
@@ -424,7 +420,6 @@ func TestPartitionAddIndexGC(t *testing.T) {
 	s := createFailDBSuite(t)
 	tk := testkit.NewTestKit(t, s.store)
 	tk.MustExec("use test")
-	tk.MustExec("set global tidb_ddl_enable_fast_reorg = 0;")
 	tk.MustExec(`create table partition_add_idx (
 	id int not null,
 	hired date not null
diff --git a/ddl/index.go b/ddl/index.go
index c3c3ffd37c926..818dc1eac7738 100644
--- a/ddl/index.go
+++ b/ddl/index.go
@@ -753,13 +753,15 @@ func IngestJobsNotExisted(ctx sessionctx.Context) bool {
 }
 
 // tryFallbackToTxnMerge changes the reorg type to txn-merge if the lightning backfill meets something wrong.
-func tryFallbackToTxnMerge(job *model.Job, err error) {
+func tryFallbackToTxnMerge(job *model.Job, err error) error {
 	if job.State != model.JobStateRollingback {
 		logutil.BgLogger().Info("[ddl] fallback to txn-merge backfill process", zap.Error(err))
 		job.ReorgMeta.ReorgTp = model.ReorgTypeTxnMerge
 		job.SnapshotVer = 0
 		job.RowCount = 0
+		return nil
 	}
+	return err
 }
 
 func doReorgWorkForCreateIndexMultiSchema(w *worker, d *ddlCtx, t *meta.Meta, job *model.Job,
@@ -801,13 +803,13 @@ func doReorgWorkForCreateIndex(w *worker, d *ddlCtx, t *meta.Meta, job *model.Jo
 			}
 			bc, err = ingest.LitBackCtxMgr.Register(w.ctx, indexInfo.Unique, job.ID, job.ReorgMeta.SQLMode)
 			if err != nil {
-				tryFallbackToTxnMerge(job, err)
+				err = tryFallbackToTxnMerge(job, err)
 				return false, ver, errors.Trace(err)
 			}
 			done, ver, err = runReorgJobAndHandleErr(w, d, t, job, tbl, indexInfo, false)
 			if err != nil {
 				ingest.LitBackCtxMgr.Unregister(job.ID)
-				tryFallbackToTxnMerge(job, err)
+				err = tryFallbackToTxnMerge(job, err)
 				return false, ver, errors.Trace(err)
 			}
 			if !done {
@@ -820,7 +822,7 @@ func doReorgWorkForCreateIndex(w *worker, d *ddlCtx, t *meta.Meta, job *model.Jo
 					ver, err = convertAddIdxJob2RollbackJob(d, t, job, tbl.Meta(), indexInfo, err)
 				} else {
 					logutil.BgLogger().Warn("[ddl] lightning import error", zap.Error(err))
-					tryFallbackToTxnMerge(job, err)
+					err = tryFallbackToTxnMerge(job, err)
 				}
 				ingest.LitBackCtxMgr.Unregister(job.ID)
 				return false, ver, errors.Trace(err)
diff --git a/ddl/ingest/env.go b/ddl/ingest/env.go
index 185f873b820a4..6e482523ad84a 100644
--- a/ddl/ingest/env.go
+++ b/ddl/ingest/env.go
@@ -47,6 +47,13 @@ const maxMemoryQuota = 2 * size.GB
 // InitGlobalLightningEnv initialize Lightning backfill environment.
 func InitGlobalLightningEnv() {
 	log.SetAppLogger(logutil.BgLogger())
+	globalCfg := config.GetGlobalConfig()
+	if globalCfg.Store != "tikv" {
+		logutil.BgLogger().Warn(LitWarnEnvInitFail,
+			zap.String("storage limitation", "only support TiKV storage"),
+			zap.String("current storage", globalCfg.Store),
+			zap.Bool("lightning is initialized", LitInitialized))
+	}
 	sPath, err := genLightningDataDir()
 	if err != nil {
 		logutil.BgLogger().Warn(LitWarnEnvInitFail, zap.Error(err),
diff --git a/ddl/multi_schema_change_test.go b/ddl/multi_schema_change_test.go
index d48aa6752f8ee..f302737d60c3b 100644
--- a/ddl/multi_schema_change_test.go
+++ b/ddl/multi_schema_change_test.go
@@ -568,8 +568,6 @@ func TestMultiSchemaChangeAddIndexesCancelled(t *testing.T) {
 	store, dom := testkit.CreateMockStoreAndDomain(t)
 	tk := testkit.NewTestKit(t, store)
 	tk.MustExec("use test")
-	// TODO: will check why tidb_ddl_enable_fast_reorg could not default be on in another pr.
-	tk.MustExec("set global tidb_ddl_enable_fast_reorg = 0;")
 	originHook := dom.DDL().GetHook()
 
 	// Test cancel successfully.
diff --git a/ddl/serial_test.go b/ddl/serial_test.go
index d0f2ada6521cb..d99036ed4dc51 100644
--- a/ddl/serial_test.go
+++ b/ddl/serial_test.go
@@ -432,8 +432,6 @@ func TestCancelAddIndexPanic(t *testing.T) {
 		require.NoError(t, failpoint.Disable("github.com/pingcap/tidb/ddl/errorMockPanic"))
 	}()
 	tk.MustExec("use test")
-	// TODO: will check why tidb_ddl_enable_fast_reorg could not default be on in another pr.
-	tk.MustExec("set global tidb_ddl_enable_fast_reorg = 0;")
 	tk.MustExec("drop table if exists t")
 	tk.MustExec("create table t(c1 int, c2 int)")
 
diff --git a/ddl/stat_test.go b/ddl/stat_test.go
index 260a98ab25f6d..556b9eb5dadc7 100644
--- a/ddl/stat_test.go
+++ b/ddl/stat_test.go
@@ -52,8 +52,6 @@ func TestDDLStatsInfo(t *testing.T) {
 	tblInfo, err := testTableInfo(store, "t", 2)
 	require.NoError(t, err)
 	testCreateTable(t, ctx, d, dbInfo, tblInfo)
-	// TODO: will check why tidb_ddl_enable_fast_reorg could not default be on in another pr.
-	tk.MustExec("set global tidb_ddl_enable_fast_reorg = 0;")
 	err = sessiontxn.NewTxn(context.Background(), ctx)
 	require.NoError(t, err)