diff --git a/extern/sector-storage/ffiwrapper/sealer_cgo.go b/extern/sector-storage/ffiwrapper/sealer_cgo.go
index 1c8c7ee84..657fac08c 100644
--- a/extern/sector-storage/ffiwrapper/sealer_cgo.go
+++ b/extern/sector-storage/ffiwrapper/sealer_cgo.go
@@ -45,6 +45,10 @@ func (sb *Sealer) NewSector(ctx context.Context, sector storage.SectorRef) error
 }
 
 func (sb *Sealer) AddPiece(ctx context.Context, sector storage.SectorRef, existingPieceSizes []abi.UnpaddedPieceSize, pieceSize abi.UnpaddedPieceSize, file storage.Data) (abi.PieceInfo, error) {
+	// TODO: allow tuning those:
+	chunk := abi.PaddedPieceSize(4 << 20)
+	parallel := runtime.NumCPU()
+
 	var offset abi.UnpaddedPieceSize
 	for _, size := range existingPieceSizes {
 		offset += size
@@ -108,10 +112,16 @@ func (sb *Sealer) AddPiece(ctx context.Context, sector storage.SectorRef, existi
 
 	pr := io.TeeReader(io.LimitReader(file, int64(pieceSize)), pw)
 
-	chunk := abi.PaddedPieceSize(4 << 20)
+	throttle := make(chan []byte, parallel)
+	piecePromises := make([]func() (abi.PieceInfo, error), 0)
 
 	buf := make([]byte, chunk.Unpadded())
-	var pieceCids []abi.PieceInfo
+	for i := 0; i < parallel; i++ {
+		if abi.UnpaddedPieceSize(i)*chunk.Unpadded() >= pieceSize {
+			break // won't use this many buffers
+		}
+		throttle <- make([]byte, chunk.Unpadded())
+	}
 
 	for {
 		var read int
@@ -132,13 +142,33 @@ func (sb *Sealer) AddPiece(ctx context.Context, sector storage.SectorRef, existi
 			break
 		}
 
-		c, err := sb.pieceCid(sector.ProofType, buf[:read])
-		if err != nil {
-			return abi.PieceInfo{}, xerrors.Errorf("pieceCid error: %w", err)
-		}
-		pieceCids = append(pieceCids, abi.PieceInfo{
-			Size:     abi.UnpaddedPieceSize(len(buf[:read])).Padded(),
-			PieceCID: c,
+		done := make(chan struct{cid.Cid; error}, 1)
+		pbuf := <-throttle
+		copy(pbuf, buf[:read])
+
+		go func(read int) {
+			defer func() {
+				throttle <- pbuf
+			}()
+
+			c, err := sb.pieceCid(sector.ProofType, pbuf[:read])
+			done <- struct {cid.Cid; error }{c, err}
+		}(read)
+
+		piecePromises = append(piecePromises, func() (abi.PieceInfo, error) {
+			select {
+			case e := <-done:
+				if e.error != nil {
+					return abi.PieceInfo{}, e.error
+				}
+
+				return abi.PieceInfo{
+					Size:     abi.UnpaddedPieceSize(len(buf[:read])).Padded(),
+					PieceCID: e.Cid,
+				}, nil
+			case <-ctx.Done():
+				return abi.PieceInfo{}, ctx.Err()
+			}
 		})
 	}
 
@@ -155,8 +185,16 @@ func (sb *Sealer) AddPiece(ctx context.Context, sector storage.SectorRef, existi
 	}
 	stagedFile = nil
 
-	if len(pieceCids) == 1 {
-		return pieceCids[0], nil
+	if len(piecePromises) == 1 {
+		return piecePromises[0]()
+	}
+
+	pieceCids := make([]abi.PieceInfo, len(piecePromises))
+	for i, promise := range piecePromises {
+		pieceCids[i], err = promise()
+		if err != nil {
+			return abi.PieceInfo{}, err
+		}
 	}
 
 	pieceCID, err := ffi.GenerateUnsealedCID(sector.ProofType, pieceCids)
diff --git a/extern/sector-storage/ffiwrapper/sealer_test.go b/extern/sector-storage/ffiwrapper/sealer_test.go
index 1292a9513..9e4aa0042 100644
--- a/extern/sector-storage/ffiwrapper/sealer_test.go
+++ b/extern/sector-storage/ffiwrapper/sealer_test.go
@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"context"
 	"fmt"
+	"github.com/filecoin-project/lotus/extern/storage-sealing/lib/nullreader"
 	"io"
 	"io/ioutil"
 	"math/rand"
@@ -622,3 +623,89 @@ func TestGenerateUnsealedCID(t *testing.T) {
 		[][]byte{barr(1, 16), barr(0, 16), barr(2, 8), barr(3, 16), barr(0, 16), barr(0, 8), barr(4, 4), barr(5, 16), barr(0, 16), barr(0, 8)},
 	)
 }
+
+func TestAddPiece512M(t *testing.T) {
+	sz := abi.PaddedPieceSize(512 << 20).Unpadded()
+
+	cdir, err := ioutil.TempDir("", "sbtest-c-")
+	if err != nil {
+		t.Fatal(err)
+	}
+	miner := abi.ActorID(123)
+
+	sp := &basicfs.Provider{
+		Root: cdir,
+	}
+	sb, err := New(sp)
+	if err != nil {
+		t.Fatalf("%+v", err)
+	}
+	cleanup := func() {
+		if t.Failed() {
+			fmt.Printf("not removing %s\n", cdir)
+			return
+		}
+		if err := os.RemoveAll(cdir); err != nil {
+			t.Error(err)
+		}
+	}
+	t.Cleanup(cleanup)
+
+	r := rand.New(rand.NewSource(0x7e5))
+
+	c, err := sb.AddPiece(context.TODO(), storage.SectorRef{
+		ID:        abi.SectorID{
+			Miner:  miner,
+			Number: 0,
+		},
+		ProofType: abi.RegisteredSealProof_StackedDrg512MiBV1_1,
+	}, nil, sz, io.LimitReader(r, int64(sz)))
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	require.Equal(t, "baga6ea4seaqhyticusemlcrjhvulpfng4nint6bu3wpe5s3x4bnuj2rs47hfacy", c.PieceCID.String())
+}
+
+func BenchmarkAddPiece512M(b *testing.B) {
+	sz := abi.PaddedPieceSize(512 << 20).Unpadded()
+	b.SetBytes(int64(sz))
+
+	cdir, err := ioutil.TempDir("", "sbtest-c-")
+	if err != nil {
+		b.Fatal(err)
+	}
+	miner := abi.ActorID(123)
+
+	sp := &basicfs.Provider{
+		Root: cdir,
+	}
+	sb, err := New(sp)
+	if err != nil {
+		b.Fatalf("%+v", err)
+	}
+	cleanup := func() {
+		if b.Failed() {
+			fmt.Printf("not removing %s\n", cdir)
+			return
+		}
+		if err := os.RemoveAll(cdir); err != nil {
+			b.Error(err)
+		}
+	}
+	b.Cleanup(cleanup)
+
+	for i := 0; i < b.N; i++ {
+		c, err := sb.AddPiece(context.TODO(), storage.SectorRef{
+			ID:        abi.SectorID{
+				Miner:  miner,
+				Number: abi.SectorNumber(i),
+			},
+			ProofType: abi.RegisteredSealProof_StackedDrg512MiBV1_1,
+		}, nil, sz, io.LimitReader(&nullreader.Reader{}, int64(sz)))
+		if err != nil {
+			b.Fatal(err)
+		}
+		fmt.Println(c)
+	}
+}
\ No newline at end of file