diff --git a/lib/nullreader/reader.go b/lib/nullreader/reader.go
new file mode 100644
index 000000000..3c0a856ca
--- /dev/null
+++ b/lib/nullreader/reader.go
@@ -0,0 +1,10 @@
+package nullreader
+
+type Reader struct{}
+
+func (Reader) Read(out []byte) (int, error) {
+	for i := range out {
+		out[i] = 0
+	}
+	return len(out), nil
+}
diff --git a/lib/zerocomm/zerocomm_test.go b/lib/zerocomm/zerocomm_test.go
index 329a2b38c..a7f745d6d 100644
--- a/lib/zerocomm/zerocomm_test.go
+++ b/lib/zerocomm/zerocomm_test.go
@@ -3,44 +3,87 @@ package zerocomm
 import (
 	"bytes"
 	"fmt"
+	"io"
 	"testing"
 
+	commcid "github.com/filecoin-project/go-fil-commcid"
 	"github.com/filecoin-project/go-sectorbuilder"
 	abi "github.com/filecoin-project/specs-actors/actors/abi"
 	"github.com/ipfs/go-cid"
+
+	"github.com/filecoin-project/lotus/lib/nullreader"
 )
 
 func TestComms(t *testing.T) {
+	t.Skip("don't have enough ram") // no, but seriously, currently this needs like 3tb of /tmp
+
 	var expPieceComms [levels - skip]cid.Cid
 
 	{
 		l2, err := sectorbuilder.GeneratePieceCIDFromFile(abi.RegisteredProof_StackedDRG2KiBPoSt, bytes.NewReader(make([]byte, 127)), 127)
 		if err != nil {
-			return
+			t.Fatal(err)
 		}
 		expPieceComms[0] = l2
 	}
 
 	for i := 1; i < levels-2; i++ {
 		var err error
-		sectorbuilder.GenerateUnsealedCID()
-		expPieceComms[i], err = sectorbuilder.GenerateDataCommitment(128<<i, []sectorbuilder.PublicPieceInfo{
-			{
-				Size:  127 << (i - 1),
-				CommP: expPieceComms[i-1],
-			},
-			{
-				Size:  127 << (i - 1),
-				CommP: expPieceComms[i-1],
-			},
-		})
+		sz := abi.UnpaddedPieceSize(127 << i)
+		fmt.Println(i, sz)
+		r := io.LimitReader(&nullreader.Reader{}, int64(sz))
+
+		expPieceComms[i], err = sectorbuilder.GeneratePieceCIDFromFile(abi.RegisteredProof_StackedDRG2KiBPoSt, r, sz)
 		if err != nil {
-			panic(err)
+			t.Fatal(err)
 		}
 	}
 
 	for i, comm := range expPieceComms {
-		if string(comm[:]) != string(pieceComms[i][:]) {
+		c, err := commcid.CIDToPieceCommitmentV1(comm)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if string(c) != string(pieceComms[i][:]) {
+			t.Errorf("zero commitment %d didn't match", i)
+		}
+	}
+
+	for _, comm := range expPieceComms { // Could do codegen, but this is good enough
+		fmt.Printf("%#v,\n", comm)
+	}
+}
+
+func TestCommsSmall(t *testing.T) {
+	var expPieceComms [8]cid.Cid
+	lvls := len(expPieceComms) + skip
+
+	{
+		l2, err := sectorbuilder.GeneratePieceCIDFromFile(abi.RegisteredProof_StackedDRG2KiBPoSt, bytes.NewReader(make([]byte, 127)), 127)
+		if err != nil {
+			t.Fatal(err)
+		}
+		expPieceComms[0] = l2
+	}
+
+	for i := 1; i < lvls-2; i++ {
+		var err error
+		sz := abi.UnpaddedPieceSize(127 << i)
+		fmt.Println(i, sz)
+		r := io.LimitReader(&nullreader.Reader{}, int64(sz))
+
+		expPieceComms[i], err = sectorbuilder.GeneratePieceCIDFromFile(abi.RegisteredProof_StackedDRG2KiBPoSt, r, sz)
+		if err != nil {
+			t.Fatal(err)
+		}
+	}
+
+	for i, comm := range expPieceComms {
+		c, err := commcid.CIDToPieceCommitmentV1(comm)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if string(c) != string(pieceComms[i][:]) {
 			t.Errorf("zero commitment %d didn't match", i)
 		}
 	}
@@ -51,13 +94,13 @@ func TestComms(t *testing.T) {
 }
 
 func TestForSise(t *testing.T) {
-	exp, err := sectorbuilder.GeneratePieceCommitment(bytes.NewReader(make([]byte, 1016)), 1016)
+	exp, err := sectorbuilder.GeneratePieceCIDFromFile(abi.RegisteredProof_StackedDRG2KiBPoSt, bytes.NewReader(make([]byte, 1016)), 1016)
 	if err != nil {
 		return
 	}
 
 	actual := ForSize(1016)
-	if string(exp[:]) != string(actual[:]) {
+	if !exp.Equals(actual) {
 		t.Errorf("zero commitment didn't match")
 	}
 }
diff --git a/storage/sealing/garbage.go b/storage/sealing/garbage.go
index 0a7b33324..93446c3c6 100644
--- a/storage/sealing/garbage.go
+++ b/storage/sealing/garbage.go
@@ -7,19 +7,12 @@ import (
 	"golang.org/x/xerrors"
 
 	"github.com/filecoin-project/specs-actors/actors/abi"
+
+	"github.com/filecoin-project/lotus/lib/nullreader"
 )
 
-type nullReader struct{}
-
-func (nullReader) Read(out []byte) (int, error) {
-	for i := range out {
-		out[i] = 0
-	}
-	return len(out), nil
-}
-
 func (m *Sealing) pledgeReader(size abi.UnpaddedPieceSize) io.Reader {
-	return io.LimitReader(&nullReader{}, int64(size))
+	return io.LimitReader(&nullreader.Reader{}, int64(size))
 }
 
 func (m *Sealing) pledgeSector(ctx context.Context, sectorID abi.SectorNumber, existingPieceSizes []abi.UnpaddedPieceSize, sizes ...abi.UnpaddedPieceSize) ([]Piece, error) {