diff --git a/level/rrrr.go b/level/rrrr.go
index 267e5ae..cd935f9 100644
--- a/level/rrrr.go
+++ b/level/rrrr.go
@@ -16,8 +16,17 @@ var BpeNotAvailableErr = errors.New("bpe not available")
 var OutOfBoundsErr = errors.New("out of bounds")
 var AvailableBpeMustBeLenOneErr = errors.New("available bpe must be 1")
 var NoAvailableBpeErr = errors.New("no available bpe")
+var Bpe0PalletMustBeLenOneErr = errors.New("bpe 0 pallet must be 1")
+var RealInvalidPaletteIndexErr = errors.New("invalid palette index")
+var AvailableBpeMustBeSortedErr = errors.New("available bpe must be sorted")
+var DirectModeCantResizeErr = errors.New("direct mode cannot resize")
 
 func (r RealStorageFormat) Import(data []uint64, bpe uint8, palette []int32) (s *RealStorage, err error) {
+	if !slices.IsSorted(r.AvailableBpes) {
+		err = AvailableBpeMustBeSortedErr
+		return
+	}
+
 	if !slices.Contains(r.AvailableBpes, bpe) {
 		err = BpeNotAvailableErr
 		return
@@ -25,7 +34,13 @@ func (r RealStorageFormat) Import(data []uint64, bpe uint8, palette []int32) (s
 	s = new(RealStorage)
 	s.format = r
 	s.resize(bpe)
-	s.data = data
+	if bpe == 0 && len(palette) != 1 {
+		err = Bpe0PalletMustBeLenOneErr
+		return
+	}
+	if data != nil {
+		s.data = data
+	}
 	s.palette = palette
 	return
 }
@@ -66,15 +81,15 @@ func (r *RealStorage) resize(bpe uint8) {
 		r.maxAtCurrentBpe = 1
 		return
 	}
-	elementsPerLong := int32(64 / int(bpe))
-	numberOfLongs := int(math.Ceil(float64(r.format.Len) / float64(elementsPerLong)))
+	numberOfElements := int32(64 / int(bpe))
+	numberOfLongs := int(math.Ceil(float64(r.format.Len) / float64(numberOfElements)))
 	newData := make([]uint64, numberOfLongs)
 	mask := (uint64(1) << uint32(bpe)) - 1
 	maxAtCurrentBpe := int32(1 << bpe)
 	if r.bpe == 0 {
-		r.data = newData
 		r.bpe = bpe
-		r.elementsPerLong = elementsPerLong
+		r.elementsPerLong = numberOfElements
+		r.data = newData
 		r.mask = mask
 		r.maxAtCurrentBpe = maxAtCurrentBpe
 		return
@@ -87,15 +102,17 @@ func (r *RealStorage) resize(bpe uint8) {
 		} else {
 			v = int32((r.data[i/r.elementsPerLong] >> ((i % r.elementsPerLong) * int32(r.bpe))) & r.mask)
 		}
-		newData[i/elementsPerLong] |= uint64(v) << ((i % elementsPerLong) * int32(bpe))
+		r.data[i/r.elementsPerLong] |= uint64(v) << ((i % r.elementsPerLong) * int32(bpe))
 	}
+	if resizeDirect {
+		r.palette = nil
+	}
+	r.elementsPerLong = numberOfElements
 	r.data = newData
-	r.bpe = bpe
-	r.elementsPerLong = elementsPerLong
 	r.mask = mask
 	r.maxAtCurrentBpe = maxAtCurrentBpe
-	return
 
+	return
 }
 
 func (r *RealStorage) Get(i int32) (s int32, err error) {
@@ -103,12 +120,26 @@ func (r *RealStorage) Get(i int32) (s int32, err error) {
 		err = OutOfBoundsErr
 		return
 	}
+	if r.bpe == 0 { // single mode
+		if len(r.palette) != 1 {
+			err = Bpe0PalletMustBeLenOneErr
+			return
+		}
+		s = r.palette[0]
+		return
+	}
+
 	v := int32((r.data[i/r.elementsPerLong] >> ((i % r.elementsPerLong) * int32(r.bpe))) & r.mask)
 	if r.palette == nil { // direct
 		s = v
 		return
 	}
-	s = r.palette[v] // should allways be true cause data checking
+	if v < 0 || v >= int32(len(r.palette)) {
+		err = RealInvalidPaletteIndexErr
+		return
+	}
+
+	s = r.palette[v]
 	return
 }
 
@@ -127,13 +158,19 @@ func (r *RealStorage) Set(i int32, v int32) (err error) {
 		if iv == -1 {
 			iv, err = r.appendPalette(v)
 		}
+		v = int32(iv)
 	}
+	r.set(i, v)
 	return
 }
 
 func (r *RealStorage) appendPalette(v int32) (i int, err error) {
-	i = len(r.palette) + 1
-	if i <= int(r.maxAtCurrentBpe) {
+	i = len(r.palette)
+	if r.palette == nil {
+		err = DirectModeCantResizeErr
+		return
+	}
+	if i < int(r.maxAtCurrentBpe) {
 		r.palette = append(r.palette, v)
 		return
 	}
@@ -144,10 +181,17 @@ func (r *RealStorage) appendPalette(v int32) (i int, err error) {
 
 	bpei := slices.Index(r.format.AvailableBpes, r.bpe)
 	if bpei == len(r.format.AvailableBpes)-1 {
-		err = CannotGrowPalletErr
+		err = NoAvailableBpeErr
 		return
 	}
 	newBpe := r.format.AvailableBpes[bpei+1]
 	r.resize(newBpe)
+	if r.palette == nil {
+		i = int(v) // direct mode
+		return
+	}
+
+	r.palette = append(r.palette, v)
+	i = len(r.palette) - 1
 	return
 }
diff --git a/level/rrrr_test.go b/level/rrrr_test.go
new file mode 100644
index 0000000..a5edd1c
--- /dev/null
+++ b/level/rrrr_test.go
@@ -0,0 +1,423 @@
+package level_test
+
+import (
+	"testing"
+
+	"github.com/admin-else/strom/level"
+)
+
+func heightmapFormat() level.RealStorageFormat {
+	return level.RealStorageFormat{
+		AvailableBpes: []uint8{9},
+		BiggestDirect: true,
+		Len:           256,
+	}
+}
+
+func blockStorageFormat() level.RealStorageFormat {
+	return level.RealStorageFormat{
+		AvailableBpes: []uint8{0, 4, 5, 6, 7, 8, 15},
+		BiggestDirect: true,
+		Len:           4096,
+	}
+}
+
+func TestRealStorageImportDataDirect(t *testing.T) {
+	format := heightmapFormat()
+	data := make([]uint64, 256)
+	data[0] = 42
+
+	s, err := format.ImportDataDirect(data)
+	if err != nil {
+		t.Fatalf("ImportDataDirect failed: %v", err)
+	}
+
+	got, err := s.Get(0)
+	if err != nil {
+		t.Fatalf("Get failed: %v", err)
+	}
+	if got != 42 {
+		t.Errorf("Get(0) = %d, want 42", got)
+	}
+}
+
+func TestRealStorageImportDataDirectMultipleBpe(t *testing.T) {
+	format := level.RealStorageFormat{
+		AvailableBpes: []uint8{4, 8},
+		BiggestDirect: true,
+		Len:           256,
+	}
+
+	_, err := format.ImportDataDirect([]uint64{1})
+	if err != level.AvailableBpeMustBeLenOneErr {
+		t.Errorf("expected AvailableBpeMustBeLenOneErr, got %v", err)
+	}
+}
+
+func TestRealStorageImportUnsortedBpe(t *testing.T) {
+	format := level.RealStorageFormat{
+		AvailableBpes: []uint8{9, 4},
+		BiggestDirect: true,
+		Len:           256,
+	}
+
+	_, err := format.Import([]uint64{1}, 4, nil)
+	if err != level.AvailableBpeMustBeSortedErr {
+		t.Errorf("expected AvailableBpeMustBeSortedErr, got %v", err)
+	}
+}
+
+func TestRealStorageImportBpeNotAvailable(t *testing.T) {
+	format := heightmapFormat()
+
+	_, err := format.Import([]uint64{1}, 4, nil)
+	if err != level.BpeNotAvailableErr {
+		t.Errorf("expected BpeNotAvailableErr, got %v", err)
+	}
+}
+
+func TestRealStorageGetSet(t *testing.T) {
+	format := blockStorageFormat()
+	s, err := format.Import(nil, 4, []int32{0, 1, 2, 3})
+	if err != nil {
+		t.Fatalf("Import failed: %v", err)
+	}
+
+	s.Set(0, 1)
+	s.Set(1, 2)
+	s.Set(2, 3)
+
+	for i, want := range []int32{1, 2, 3} {
+		got, err := s.Get(int32(i))
+		if err != nil {
+			t.Fatalf("Get(%d) failed: %v", i, err)
+		}
+		if got != want {
+			t.Errorf("Get(%d) = %d, want %d", i, got, want)
+		}
+	}
+}
+
+func TestRealStorageOutOfBounds(t *testing.T) {
+	format := blockStorageFormat()
+	s, err := format.Import(nil, 4, []int32{0, 1})
+	if err != nil {
+		t.Fatalf("Import failed: %v", err)
+	}
+
+	_, err = s.Get(4096)
+	if err != level.OutOfBoundsErr {
+		t.Errorf("expected OutOfBoundsErr, got %v", err)
+	}
+
+	_, err = s.Get(-1)
+	if err != level.OutOfBoundsErr {
+		t.Errorf("expected OutOfBoundsErr, got %v", err)
+	}
+}
+
+func TestRealStorageBpeZero(t *testing.T) {
+	format := level.RealStorageFormat{
+		AvailableBpes: []uint8{0, 4, 8},
+		BiggestDirect: true,
+		Len:           64,
+	}
+
+	s, err := format.Import(nil, 0, []int32{42})
+	if err != nil {
+		t.Fatalf("Import failed: %v", err)
+	}
+
+	for i := int32(0); i < 64; i++ {
+		got, err := s.Get(i)
+		if err != nil {
+			t.Fatalf("Get(%d) failed: %v", i, err)
+		}
+		if got != 42 {
+			t.Errorf("Get(%d) = %d, want 42", i, got)
+		}
+	}
+}
+
+func TestRealStorageBpeZeroPaletteLen(t *testing.T) {
+	format := level.RealStorageFormat{
+		AvailableBpes: []uint8{0, 4, 8},
+		BiggestDirect: true,
+		Len:           64,
+	}
+
+	_, err := format.Import(nil, 0, []int32{1, 2})
+	if err != level.Bpe0PalletMustBeLenOneErr {
+		t.Errorf("expected Bpe0PalletMustBeLenOneErr, got %v", err)
+	}
+}
+
+func TestRealStorageResize(t *testing.T) {
+	format := level.RealStorageFormat{
+		AvailableBpes: []uint8{4, 8},
+		BiggestDirect: false,
+		Len:           16,
+	}
+
+	s, err := format.Import(nil, 4, []int32{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15})
+	if err != nil {
+		t.Fatalf("Import failed: %v", err)
+	}
+
+	for i := int32(0); i < 16; i++ {
+		s.Set(i, i)
+	}
+
+	for i := int32(0); i < 16; i++ {
+		got, err := s.Get(i)
+		if err != nil {
+			t.Fatalf("Get(%d) failed: %v", i, err)
+		}
+		if got != i {
+			t.Errorf("Get(%d) = %d, want %d", i, got, i)
+		}
+	}
+}
+
+func TestRealStorageResizePreservesData(t *testing.T) {
+	format := level.RealStorageFormat{
+		AvailableBpes: []uint8{4, 5, 6, 8},
+		BiggestDirect: false,
+		Len:           8,
+	}
+
+	s, err := format.Import(nil, 4, []int32{0, 1})
+	if err != nil {
+		t.Fatalf("Import failed: %v", err)
+	}
+
+	s.Set(0, 10)
+	s.Set(1, 20)
+	s.Set(2, 30)
+	s.Set(3, 40)
+
+	for i, want := range []int32{10, 20, 30, 40} {
+		got, err := s.Get(int32(i))
+		if err != nil {
+			t.Fatalf("Get(%d) failed: %v", i, err)
+		}
+		if got != want {
+			t.Errorf("Get(%d) = %d, want %d", i, got, want)
+		}
+	}
+}
+
+func TestRealStoragePaletteGrowth(t *testing.T) {
+	format := level.RealStorageFormat{
+		AvailableBpes: []uint8{4, 5, 6, 8},
+		BiggestDirect: false,
+		Len:           16,
+	}
+
+	s, err := format.Import(nil, 4, []int32{0})
+	if err != nil {
+		t.Fatalf("Import failed: %v", err)
+	}
+
+	s.Set(0, 10)
+	s.Set(1, 20)
+
+	got, err := s.Get(0)
+	if err != nil {
+		t.Fatalf("Get(0) failed: %v", err)
+	}
+	if got != 10 {
+		t.Errorf("Get(0) = %d, want 10", got)
+	}
+
+	got, err = s.Get(1)
+	if err != nil {
+		t.Fatalf("Get(1) failed: %v", err)
+	}
+	if got != 20 {
+		t.Errorf("Get(1) = %d, want 20", got)
+	}
+}
+
+func TestRealStorageNoAvailableBpe(t *testing.T) {
+	format := level.RealStorageFormat{
+		AvailableBpes: []uint8{4},
+		BiggestDirect: false,
+		Len:           16,
+	}
+
+	s, err := format.Import(nil, 4, []int32{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15})
+	if err != nil {
+		t.Fatalf("Import failed: %v", err)
+	}
+
+	err = s.Set(0, 16)
+	if err != level.NoAvailableBpeErr {
+		t.Errorf("expected NoAvailableBpeErr, got %v", err)
+	}
+}
+
+func TestRealStorageBiggestDirect(t *testing.T) {
+	format := level.RealStorageFormat{
+		AvailableBpes: []uint8{4, 8},
+		BiggestDirect: true,
+		Len:           64,
+	}
+
+	s, err := format.Import(nil, 8, nil)
+	if err != nil {
+		t.Fatalf("Import failed: %v", err)
+	}
+
+	for i := int32(0); i < 64; i++ {
+		s.Set(i, i)
+	}
+
+	for i := int32(0); i < 64; i++ {
+		got, err := s.Get(i)
+		if err != nil {
+			t.Fatalf("Get(%d) failed: %v", i, err)
+		}
+		if got != i {
+			t.Errorf("Get(%d) = %d, want %d", i, got, i)
+		}
+	}
+}
+
+func TestRealStorageDirectModeNoPalette(t *testing.T) {
+	format := level.RealStorageFormat{
+		AvailableBpes: []uint8{9},
+		BiggestDirect: true,
+		Len:           256,
+	}
+
+	data := make([]uint64, 36)
+	data[0] = 0x1FFFF
+
+	s, err := format.ImportDataDirect(data)
+	if err != nil {
+		t.Fatalf("ImportDataDirect failed: %v", err)
+	}
+
+	got, err := s.Get(0)
+	if err != nil {
+		t.Fatalf("Get(0) failed: %v", err)
+	}
+	if got != 0x1FFFF {
+		t.Errorf("Get(0) = %d, want %d", got, 0x1FFFF)
+	}
+}
+
+func TestRealStorageInvalidPaletteIndex(t *testing.T) {
+	format := level.RealStorageFormat{
+		AvailableBpes: []uint8{4, 8},
+		BiggestDirect: false,
+		Len:           16,
+	}
+
+	data := []uint64{0xFFFF}
+	s, err := format.Import(data, 4, []int32{0, 1})
+	if err != nil {
+		t.Fatalf("Import failed: %v", err)
+	}
+
+	_, err = s.Get(0)
+	if err != level.RealInvalidPaletteIndexErr {
+		t.Errorf("expected RealInvalidPaletteIndexErr, got %v", err)
+	}
+}
+
+func TestRealStorageOverwrite(t *testing.T) {
+	format := blockStorageFormat()
+	s, err := format.Import(nil, 4, []int32{0, 1, 2})
+	if err != nil {
+		t.Fatalf("Import failed: %v", err)
+	}
+
+	s.Set(0, 1)
+	s.Set(0, 2)
+	s.Set(0, 1)
+
+	got, err := s.Get(0)
+	if err != nil {
+		t.Fatalf("Get(0) failed: %v", err)
+	}
+	if got != 1 {
+		t.Errorf("Get(0) = %d, want 1", got)
+	}
+}
+
+func TestRealStorageSetOutOfBounds(t *testing.T) {
+	format := blockStorageFormat()
+	s, err := format.Import(nil, 4, []int32{0, 1})
+	if err != nil {
+		t.Fatalf("Import failed: %v", err)
+	}
+
+	err = s.Set(4096, 1)
+	if err != level.OutOfBoundsErr {
+		t.Errorf("expected OutOfBoundsErr, got %v", err)
+	}
+
+	err = s.Set(-1, 1)
+	if err != level.OutOfBoundsErr {
+		t.Errorf("expected OutOfBoundsErr, got %v", err)
+	}
+}
+
+func TestRealStorageGetAfterResize(t *testing.T) {
+	format := level.RealStorageFormat{
+		AvailableBpes: []uint8{4, 5, 6, 8},
+		BiggestDirect: false,
+		Len:           32,
+	}
+
+	s, err := format.Import(nil, 4, []int32{0})
+	if err != nil {
+		t.Fatalf("Import failed: %v", err)
+	}
+
+	for i := int32(0); i < 16; i++ {
+		s.Set(i, i)
+	}
+
+	for i := int32(0); i < 16; i++ {
+		got, err := s.Get(i)
+		if err != nil {
+			t.Fatalf("Get(%d) failed: %v", i, err)
+		}
+		if got != i {
+			t.Errorf("Get(%d) = %d, want %d", i, got, i)
+		}
+	}
+}
+
+func TestRealStorageResizeDirect(t *testing.T) {
+	format := level.RealStorageFormat{
+		AvailableBpes: []uint8{4, 8},
+		BiggestDirect: true,
+		Len:           64,
+	}
+
+	s, err := format.Import(nil, 4, []int32{})
+	if err != nil {
+		t.Fatalf("Import failed: %v", err)
+	}
+
+	for i := int32(0); i < 64; i++ {
+		err = s.Set(i, i)
+		if err != nil {
+			t.Fatalf("Set(%d) failed: %v", i, err)
+		}
+	}
+
+	for i := int32(0); i < 64; i++ {
+		got, err := s.Get(i)
+		if err != nil {
+			t.Fatalf("Get(%d) failed: %v", i, err)
+		}
+		if got != i {
+			t.Errorf("Get(%d) = %d, want %d", i, got, i)
+		}
+	}
+}