diff --git a/extern/sector-storage/mock/mock.go b/extern/sector-storage/mock/mock.go
index eeb1404ad..4d0592d36 100644
--- a/extern/sector-storage/mock/mock.go
+++ b/extern/sector-storage/mock/mock.go
@@ -12,6 +12,7 @@ import (
 
 	proof5 "github.com/filecoin-project/specs-actors/v5/actors/runtime/proof"
 
+	"github.com/filecoin-project/dagstore/mount"
 	ffiwrapper2 "github.com/filecoin-project/go-commp-utils/ffiwrapper"
 	commcid "github.com/filecoin-project/go-fil-commcid"
 	"github.com/filecoin-project/go-state-types/abi"
@@ -384,12 +385,20 @@ func generateFakePoSt(sectorInfo []proof5.SectorInfo, rpt func(abi.RegisteredSea
 	}
 }
 
-func (mgr *SectorMgr) ReadPiece(ctx context.Context, sector storage.SectorRef, offset storiface.UnpaddedByteIndex, startOffset uint64, size abi.UnpaddedPieceSize, ticket abi.SealRandomness, unsealed cid.Cid) (io.ReadCloser, bool, error) {
+func (mgr *SectorMgr) ReadPiece(ctx context.Context, sector storage.SectorRef, offset storiface.UnpaddedByteIndex, size abi.UnpaddedPieceSize, ticket abi.SealRandomness, unsealed cid.Cid) (mount.Reader, bool, error) {
 	if uint64(offset) != 0 {
 		panic("implme")
 	}
 
-	return ioutil.NopCloser(bytes.NewReader(mgr.pieces[mgr.sectors[sector.ID].pieces[0]][startOffset:size])), false, nil
+	return struct {
+		io.ReadCloser
+		io.Seeker
+		io.ReaderAt
+	}{
+		ReadCloser: ioutil.NopCloser(bytes.NewReader(mgr.pieces[mgr.sectors[sector.ID].pieces[0]][:size])),
+		Seeker:     nil,
+		ReaderAt:   nil,
+	}, false, nil
 }
 
 func (mgr *SectorMgr) StageFakeData(mid abi.ActorID, spt abi.RegisteredSealProof) (storage.SectorRef, []abi.PieceInfo, error) {
diff --git a/extern/sector-storage/piece_provider.go b/extern/sector-storage/piece_provider.go
index aa2ef0d0d..c500b4e30 100644
--- a/extern/sector-storage/piece_provider.go
+++ b/extern/sector-storage/piece_provider.go
@@ -8,6 +8,7 @@ import (
 	"github.com/ipfs/go-cid"
 	"golang.org/x/xerrors"
 
+	"github.com/filecoin-project/dagstore/mount"
 	"github.com/filecoin-project/go-state-types/abi"
 	"github.com/filecoin-project/specs-storage/storage"
 
@@ -27,7 +28,7 @@ type PieceProvider interface {
 	//  default in most cases, but this might matter with future PoRep)
 	// startOffset is added to the pieceOffset to get the starting reader offset.
 	// The number of bytes that can be read is pieceSize-startOffset
-	ReadPiece(ctx context.Context, sector storage.SectorRef, pieceOffset storiface.UnpaddedByteIndex, startOffset uint64, pieceSize abi.UnpaddedPieceSize, ticket abi.SealRandomness, unsealed cid.Cid) (io.ReadCloser, bool, error)
+	ReadPiece(ctx context.Context, sector storage.SectorRef, pieceOffset storiface.UnpaddedByteIndex, pieceSize abi.UnpaddedPieceSize, ticket abi.SealRandomness, unsealed cid.Cid) (mount.Reader, bool, error)
 	IsUnsealed(ctx context.Context, sector storage.SectorRef, offset storiface.UnpaddedByteIndex, size abi.UnpaddedPieceSize) (bool, error)
 }
 
@@ -71,28 +72,62 @@ func (p *pieceProvider) IsUnsealed(ctx context.Context, sector storage.SectorRef
 // It will NOT try to schedule an Unseal of a sealed sector file for the read.
 //
 // Returns a nil reader if the piece does NOT exist in any unsealed file or there is no unsealed file for the given sector on any of the workers.
-func (p *pieceProvider) tryReadUnsealedPiece(ctx context.Context, sector storage.SectorRef, pieceOffset, startOffset storiface.UnpaddedByteIndex, size abi.UnpaddedPieceSize) (io.ReadCloser, context.CancelFunc, error) {
+func (p *pieceProvider) tryReadUnsealedPiece(ctx context.Context, pc cid.Cid, sector storage.SectorRef, pieceOffset storiface.UnpaddedByteIndex, size abi.UnpaddedPieceSize) (mount.Reader, error) {
 	// acquire a lock purely for reading unsealed sectors
 	ctx, cancel := context.WithCancel(ctx)
 	if err := p.index.StorageLock(ctx, sector.ID, storiface.FTUnsealed, storiface.FTNone); err != nil {
 		cancel()
-		return nil, nil, xerrors.Errorf("acquiring read sector lock: %w", err)
+		return nil, xerrors.Errorf("acquiring read sector lock: %w", err)
 	}
 
-	// Reader returns a reader for an unsealed piece at the given offset in the given sector.
-	// The returned reader will be nil if none of the workers has an unsealed sector file containing
-	// the unsealed piece.
-	r, err := p.storage.Reader(ctx, sector, abi.PaddedPieceSize(pieceOffset.Padded()+startOffset.Padded()), size.Padded()-abi.PaddedPieceSize(startOffset.Padded()))
-	if err != nil {
-		log.Debugf("did not get storage reader;sector=%+v, err:%s", sector.ID, err)
-		cancel()
-		return nil, nil, err
-	}
-	if r == nil {
+	pr, err := (&pieceReader{
+		ctx: ctx,
+		getReader: func(ctx context.Context, startOffset uint64) (io.ReadCloser, error) {
+			startOffsetAligned := storiface.UnpaddedByteIndex(startOffset / 127 * 127) // floor to multiple of 127
+
+			// Reader returns a reader for an unsealed piece at the given offset in the given sector.
+			// The returned reader will be nil if none of the workers has an unsealed sector file containing
+			// the unsealed piece.
+			r, err := p.storage.Reader(ctx, sector, abi.PaddedPieceSize(pieceOffset.Padded()+startOffsetAligned.Padded()), size.Padded()-abi.PaddedPieceSize(startOffsetAligned.Padded()))
+			if err != nil {
+				log.Debugf("did not get storage reader;sector=%+v, err:%s", sector.ID, err)
+				return nil, err
+			}
+			if r == nil {
+				return nil, nil
+			}
+
+			upr, err := fr32.NewUnpadReader(r, size.Padded())
+			if err != nil {
+				r.Close() // nolint
+				return nil, xerrors.Errorf("creating unpadded reader: %w", err)
+			}
+
+			bir := bufio.NewReaderSize(upr, 127)
+			if startOffset > uint64(startOffsetAligned) {
+				if _, err := bir.Discard(int(startOffset - uint64(startOffsetAligned))); err != nil {
+					return nil, xerrors.Errorf("discarding bytes for startOffset: %w", err)
+				}
+			}
+
+			return struct {
+				io.Reader
+				io.Closer
+			}{
+				Reader: bir,
+				Closer: r,
+			}, nil
+		},
+		len:      size,
+		onClose:  cancel,
+		pieceCid: pc,
+	}).init()
+	if err != nil || pr == nil { // pr == nil to make sure we don't return typed nil
 		cancel()
+		return nil, err
 	}
 
-	return r, cancel, nil
+	return pr, err
 }
 
 // ReadPiece is used to read an Unsealed piece at the given offset and of the given size from a Sector
@@ -101,7 +136,7 @@ func (p *pieceProvider) tryReadUnsealedPiece(ctx context.Context, sector storage
 // If we do NOT have an existing unsealed file  containing the given piece thus causing us to schedule an Unseal,
 // the returned boolean parameter will be set to true.
 // If we have an existing unsealed file containing the given piece, the returned boolean will be set to false.
-func (p *pieceProvider) ReadPiece(ctx context.Context, sector storage.SectorRef, pieceOffset storiface.UnpaddedByteIndex, startOffset uint64, size abi.UnpaddedPieceSize, ticket abi.SealRandomness, unsealed cid.Cid) (io.ReadCloser, bool, error) {
+func (p *pieceProvider) ReadPiece(ctx context.Context, sector storage.SectorRef, pieceOffset storiface.UnpaddedByteIndex, size abi.UnpaddedPieceSize, ticket abi.SealRandomness, unsealed cid.Cid) (mount.Reader, bool, error) {
 	if err := pieceOffset.Valid(); err != nil {
 		return nil, false, xerrors.Errorf("pieceOffset is not valid: %w", err)
 	}
@@ -109,9 +144,7 @@ func (p *pieceProvider) ReadPiece(ctx context.Context, sector storage.SectorRef,
 		return nil, false, xerrors.Errorf("size is not a valid piece size: %w", err)
 	}
 
-	startOffsetAligned := storiface.UnpaddedByteIndex(startOffset / 127 * 127) // floor to multiple of 127
-
-	r, unlock, err := p.tryReadUnsealedPiece(ctx, sector, pieceOffset, startOffsetAligned, size)
+	r, err := p.tryReadUnsealedPiece(ctx, unsealed, sector, pieceOffset, size)
 
 	log.Debugf("result of first tryReadUnsealedPiece: r=%+v, err=%s", r, err)
 
@@ -142,7 +175,7 @@ func (p *pieceProvider) ReadPiece(ctx context.Context, sector storage.SectorRef,
 
 		log.Debugf("unsealed a sector file to read the piece, sector=%+v, pieceOffset=%d, size=%d", sector, pieceOffset, size)
 
-		r, unlock, err = p.tryReadUnsealedPiece(ctx, sector, pieceOffset, startOffsetAligned, size)
+		r, err = p.tryReadUnsealedPiece(ctx, unsealed, sector, pieceOffset, size)
 		if err != nil {
 			log.Errorf("failed to tryReadUnsealedPiece after SectorsUnsealPiece: %s", err)
 			return nil, true, xerrors.Errorf("read after unsealing: %w", err)
@@ -156,34 +189,7 @@ func (p *pieceProvider) ReadPiece(ctx context.Context, sector storage.SectorRef,
 		log.Debugf("unsealed piece already exists, no need to unseal, sector=%+v, pieceOffset=%d, size=%d", sector, pieceOffset, size)
 	}
 
-	upr, err := fr32.NewUnpadReader(r, size.Padded())
-	if err != nil {
-		unlock()
-		return nil, uns, xerrors.Errorf("creating unpadded reader: %w", err)
-	}
+	log.Debugf("returning reader to read unsealed piece, sector=%+v, pieceOffset=%d, size=%d", sector, pieceOffset, size)
 
-	log.Debugf("returning reader to read unsealed piece, sector=%+v, pieceOffset=%d, startOffset=%d, size=%d", sector, pieceOffset, startOffset, size)
-
-	bir := bufio.NewReaderSize(upr, 127)
-	if startOffset > uint64(startOffsetAligned) {
-		if _, err := bir.Discard(int(startOffset - uint64(startOffsetAligned))); err != nil {
-			return nil, false, xerrors.Errorf("discarding bytes for startOffset: %w", err)
-		}
-	}
-
-	return &funcCloser{
-		Reader: bir,
-		close: func() error {
-			err = r.Close()
-			unlock()
-			return err
-		},
-	}, uns, nil
+	return r, uns, nil
 }
-
-type funcCloser struct {
-	io.Reader
-	close func() error
-}
-
-func (fc *funcCloser) Close() error { return fc.close() }
diff --git a/extern/sector-storage/piece_provider_test.go b/extern/sector-storage/piece_provider_test.go
index 1aad3d2d2..3ace2916e 100644
--- a/extern/sector-storage/piece_provider_test.go
+++ b/extern/sector-storage/piece_provider_test.go
@@ -338,7 +338,7 @@ func (p *pieceProviderTestHarness) isUnsealed(t *testing.T, offset storiface.Unp
 
 func (p *pieceProviderTestHarness) readPiece(t *testing.T, offset storiface.UnpaddedByteIndex, size abi.UnpaddedPieceSize,
 	expectedHadToUnseal bool, expectedBytes []byte) {
-	rd, isUnsealed, err := p.pp.ReadPiece(p.ctx, p.sector, offset, 0, size, p.ticket, p.commD)
+	rd, isUnsealed, err := p.pp.ReadPiece(p.ctx, p.sector, offset, size, p.ticket, p.commD)
 	require.NoError(t, err)
 	require.NotNil(t, rd)
 	require.Equal(t, expectedHadToUnseal, isUnsealed)
diff --git a/markets/dagstore/piecereader.go b/extern/sector-storage/piece_reader.go
similarity index 90%
rename from markets/dagstore/piecereader.go
rename to extern/sector-storage/piece_reader.go
index 67cd10c27..14f13f017 100644
--- a/markets/dagstore/piecereader.go
+++ b/extern/sector-storage/piece_reader.go
@@ -1,4 +1,4 @@
-package dagstore
+package sectorstorage
 
 import (
 	"bufio"
@@ -19,11 +19,14 @@ import (
 var MaxPieceReaderBurnBytes int64 = 1 << 20 // 1M
 var ReadBuf = 128 * (127 * 8)               // unpadded(128k)
 
+type pieceGetter func(ctx context.Context, offset uint64) (io.ReadCloser, error)
+
 type pieceReader struct {
-	ctx      context.Context
-	api      MinerAPI
-	pieceCid cid.Cid
-	len      abi.UnpaddedPieceSize
+	ctx       context.Context
+	getReader pieceGetter
+	pieceCid  cid.Cid
+	len       abi.UnpaddedPieceSize
+	onClose   context.CancelFunc
 
 	closed bool
 	seqAt  int64 // next byte to be read by io.Reader
@@ -37,10 +40,14 @@ func (p *pieceReader) init() (_ *pieceReader, err error) {
 	stats.Record(p.ctx, metrics.DagStorePRInitCount.M(1))
 
 	p.rAt = 0
-	p.r, p.len, err = p.api.FetchUnsealedPiece(p.ctx, p.pieceCid, uint64(p.rAt))
+	p.r, err = p.getReader(p.ctx, uint64(p.rAt))
 	if err != nil {
 		return nil, err
 	}
+	if p.r == nil {
+		return nil, nil
+	}
+
 	p.br = bufio.NewReaderSize(p.r, ReadBuf)
 
 	return p, nil
@@ -66,6 +73,10 @@ func (p *pieceReader) Close() error {
 		p.r = nil
 	}
 
+	p.onClose()
+
+	p.closed = true
+
 	return nil
 }
 
@@ -127,7 +138,7 @@ func (p *pieceReader) ReadAt(b []byte, off int64) (n int, err error) {
 		}
 
 		p.rAt = off
-		p.r, _, err = p.api.FetchUnsealedPiece(p.ctx, p.pieceCid, uint64(p.rAt))
+		p.r, err = p.getReader(p.ctx, uint64(p.rAt))
 		p.br = bufio.NewReaderSize(p.r, ReadBuf)
 		if err != nil {
 			return 0, xerrors.Errorf("getting backing reader: %w", err)
diff --git a/markets/dagstore/miner_api.go b/markets/dagstore/miner_api.go
index d59a05846..7f59162f0 100644
--- a/markets/dagstore/miner_api.go
+++ b/markets/dagstore/miner_api.go
@@ -3,22 +3,21 @@ package dagstore
 import (
 	"context"
 	"fmt"
-	"io"
-
-	"github.com/filecoin-project/dagstore/throttle"
-	"github.com/filecoin-project/go-state-types/abi"
 	"github.com/ipfs/go-cid"
 	"golang.org/x/xerrors"
 
+	"github.com/filecoin-project/dagstore/mount"
+	"github.com/filecoin-project/dagstore/throttle"
 	"github.com/filecoin-project/go-fil-markets/piecestore"
 	"github.com/filecoin-project/go-fil-markets/retrievalmarket"
 	"github.com/filecoin-project/go-fil-markets/shared"
+	"github.com/filecoin-project/go-state-types/abi"
 )
 
 //go:generate go run github.com/golang/mock/mockgen -destination=mocks/mock_lotus_accessor.go -package=mock_dagstore . MinerAPI
 
 type MinerAPI interface {
-	FetchUnsealedPiece(ctx context.Context, pieceCid cid.Cid, offset uint64) (io.ReadCloser, abi.UnpaddedPieceSize, error)
+	FetchUnsealedPiece(ctx context.Context, pieceCid cid.Cid) (mount.Reader, error)
 	GetUnpaddedCARSize(ctx context.Context, pieceCid cid.Cid) (uint64, error)
 	IsUnsealed(ctx context.Context, pieceCid cid.Cid) (bool, error)
 	Start(ctx context.Context) error
@@ -27,7 +26,7 @@ type MinerAPI interface {
 type SectorAccessor interface {
 	retrievalmarket.SectorAccessor
 
-	UnsealSectorAt(ctx context.Context, sectorID abi.SectorNumber, pieceOffset abi.UnpaddedPieceSize, startOffset uint64, length abi.UnpaddedPieceSize) (io.ReadCloser, error)
+	UnsealSectorAt(ctx context.Context, sectorID abi.SectorNumber, pieceOffset abi.UnpaddedPieceSize, length abi.UnpaddedPieceSize) (mount.Reader, error)
 }
 
 type minerAPI struct {
@@ -100,10 +99,10 @@ func (m *minerAPI) IsUnsealed(ctx context.Context, pieceCid cid.Cid) (bool, erro
 	return false, nil
 }
 
-func (m *minerAPI) FetchUnsealedPiece(ctx context.Context, pieceCid cid.Cid, offset uint64) (io.ReadCloser, abi.UnpaddedPieceSize, error) {
+func (m *minerAPI) FetchUnsealedPiece(ctx context.Context, pieceCid cid.Cid) (mount.Reader, error) {
 	err := m.readyMgr.AwaitReady()
 	if err != nil {
-		return nil, 0, err
+		return nil, err
 	}
 
 	// Throttle this path to avoid flooding the storage subsystem.
@@ -114,11 +113,11 @@ func (m *minerAPI) FetchUnsealedPiece(ctx context.Context, pieceCid cid.Cid, off
 	})
 
 	if err != nil {
-		return nil, 0, xerrors.Errorf("failed to fetch pieceInfo for piece %s: %w", pieceCid, err)
+		return nil, xerrors.Errorf("failed to fetch pieceInfo for piece %s: %w", pieceCid, err)
 	}
 
 	if len(pieceInfo.Deals) == 0 {
-		return nil, 0, xerrors.Errorf("no storage deals found for piece %s", pieceCid)
+		return nil, xerrors.Errorf("no storage deals found for piece %s", pieceCid)
 	}
 
 	// prefer an unsealed sector containing the piece if one exists
@@ -126,7 +125,7 @@ func (m *minerAPI) FetchUnsealedPiece(ctx context.Context, pieceCid cid.Cid, off
 		deal := deal
 
 		// Throttle this path to avoid flooding the storage subsystem.
-		var reader io.ReadCloser
+		var reader mount.Reader
 		err := m.throttle.Do(ctx, func(ctx context.Context) (err error) {
 			isUnsealed, err := m.sa.IsUnsealed(ctx, deal.SectorID, deal.Offset.Unpadded(), deal.Length.Unpadded())
 			if err != nil {
@@ -136,7 +135,7 @@ func (m *minerAPI) FetchUnsealedPiece(ctx context.Context, pieceCid cid.Cid, off
 				return nil
 			}
 			// Because we know we have an unsealed copy, this UnsealSector call will actually not perform any unsealing.
-			reader, err = m.sa.UnsealSectorAt(ctx, deal.SectorID, deal.Offset.Unpadded(), offset, deal.Length.Unpadded())
+			reader, err = m.sa.UnsealSectorAt(ctx, deal.SectorID, deal.Offset.Unpadded(), deal.Length.Unpadded())
 			return err
 		})
 
@@ -147,7 +146,7 @@ func (m *minerAPI) FetchUnsealedPiece(ctx context.Context, pieceCid cid.Cid, off
 
 		if reader != nil {
 			// we were able to obtain a reader for an already unsealed piece
-			return reader, deal.Length.Unpadded(), nil
+			return reader, nil
 		}
 	}
 
@@ -158,7 +157,7 @@ func (m *minerAPI) FetchUnsealedPiece(ctx context.Context, pieceCid cid.Cid, off
 		// block for a long time with the current PoRep
 		//
 		// This path is unthrottled.
-		reader, err := m.sa.UnsealSectorAt(ctx, deal.SectorID, deal.Offset.Unpadded(), offset, deal.Length.Unpadded())
+		reader, err := m.sa.UnsealSectorAt(ctx, deal.SectorID, deal.Offset.Unpadded(), deal.Length.Unpadded())
 		if err != nil {
 			lastErr = xerrors.Errorf("failed to unseal deal %d: %w", deal.DealID, err)
 			log.Warn(lastErr.Error())
@@ -166,10 +165,10 @@ func (m *minerAPI) FetchUnsealedPiece(ctx context.Context, pieceCid cid.Cid, off
 		}
 
 		// Successfully fetched the deal data so return a reader over the data
-		return reader, deal.Length.Unpadded(), nil
+		return reader, nil
 	}
 
-	return nil, 0, lastErr
+	return nil, lastErr
 }
 
 func (m *minerAPI) GetUnpaddedCARSize(ctx context.Context, pieceCid cid.Cid) (uint64, error) {
diff --git a/markets/dagstore/miner_api_test.go b/markets/dagstore/miner_api_test.go
index 38c3a4fc3..45cbf2461 100644
--- a/markets/dagstore/miner_api_test.go
+++ b/markets/dagstore/miner_api_test.go
@@ -15,6 +15,7 @@ import (
 	"github.com/stretchr/testify/require"
 	"golang.org/x/sync/errgroup"
 
+	"github.com/filecoin-project/dagstore/mount"
 	"github.com/filecoin-project/go-address"
 	"github.com/filecoin-project/go-state-types/abi"
 	"github.com/filecoin-project/specs-actors/actors/builtin/paych"
@@ -87,7 +88,7 @@ func TestLotusAccessorFetchUnsealedPiece(t *testing.T) {
 			}
 
 			// Fetch the piece
-			r, _, err := api.FetchUnsealedPiece(ctx, cid1, 0)
+			r, err := api.FetchUnsealedPiece(ctx, cid1)
 			if tc.expectErr {
 				require.Error(t, err)
 				return
@@ -159,7 +160,7 @@ func TestThrottle(t *testing.T) {
 	errgrp, ctx := errgroup.WithContext(context.Background())
 	for i := 0; i < 10; i++ {
 		errgrp.Go(func() error {
-			r, _, err := api.FetchUnsealedPiece(ctx, cid1, 0)
+			r, err := api.FetchUnsealedPiece(ctx, cid1)
 			if err == nil {
 				_ = r.Close()
 			}
@@ -203,10 +204,10 @@ type mockRPN struct {
 }
 
 func (m *mockRPN) UnsealSector(ctx context.Context, sectorID abi.SectorNumber, offset abi.UnpaddedPieceSize, length abi.UnpaddedPieceSize) (io.ReadCloser, error) {
-	return m.UnsealSectorAt(ctx, sectorID, offset, 0, length)
+	return m.UnsealSectorAt(ctx, sectorID, offset, length)
 }
 
-func (m *mockRPN) UnsealSectorAt(ctx context.Context, sectorID abi.SectorNumber, pieceOffset abi.UnpaddedPieceSize, startOffset uint64, length abi.UnpaddedPieceSize) (io.ReadCloser, error) {
+func (m *mockRPN) UnsealSectorAt(ctx context.Context, sectorID abi.SectorNumber, pieceOffset abi.UnpaddedPieceSize, length abi.UnpaddedPieceSize) (mount.Reader, error) {
 	atomic.AddInt32(&m.calls, 1)
 	m.lk.RLock()
 	defer m.lk.RUnlock()
@@ -215,7 +216,13 @@ func (m *mockRPN) UnsealSectorAt(ctx context.Context, sectorID abi.SectorNumber,
 	if !ok {
 		panic("sector not found")
 	}
-	return io.NopCloser(bytes.NewBuffer([]byte(data[startOffset:]))), nil
+	return struct {
+		io.ReadCloser
+		io.ReaderAt
+		io.Seeker
+	}{
+		ReadCloser: io.NopCloser(bytes.NewBuffer([]byte(data[:]))),
+	}, nil
 }
 
 func (m *mockRPN) IsUnsealed(ctx context.Context, sectorID abi.SectorNumber, offset abi.UnpaddedPieceSize, length abi.UnpaddedPieceSize) (bool, error) {
diff --git a/markets/dagstore/mocks/mock_lotus_accessor.go b/markets/dagstore/mocks/mock_lotus_accessor.go
index e10a1b053..19923cc2a 100644
--- a/markets/dagstore/mocks/mock_lotus_accessor.go
+++ b/markets/dagstore/mocks/mock_lotus_accessor.go
@@ -6,10 +6,9 @@ package mock_dagstore
 
 import (
 	context "context"
-	io "io"
 	reflect "reflect"
 
-	abi "github.com/filecoin-project/go-state-types/abi"
+	mount "github.com/filecoin-project/dagstore/mount"
 	gomock "github.com/golang/mock/gomock"
 	cid "github.com/ipfs/go-cid"
 )
@@ -38,19 +37,18 @@ func (m *MockMinerAPI) EXPECT() *MockMinerAPIMockRecorder {
 }
 
 // FetchUnsealedPiece mocks base method.
-func (m *MockMinerAPI) FetchUnsealedPiece(arg0 context.Context, arg1 cid.Cid, arg2 uint64) (io.ReadCloser, abi.UnpaddedPieceSize, error) {
+func (m *MockMinerAPI) FetchUnsealedPiece(arg0 context.Context, arg1 cid.Cid) (mount.Reader, error) {
 	m.ctrl.T.Helper()
-	ret := m.ctrl.Call(m, "FetchUnsealedPiece", arg0, arg1, arg2)
-	ret0, _ := ret[0].(io.ReadCloser)
-	ret1, _ := ret[1].(abi.UnpaddedPieceSize)
-	ret2, _ := ret[2].(error)
-	return ret0, ret1, ret2
+	ret := m.ctrl.Call(m, "FetchUnsealedPiece", arg0, arg1)
+	ret0, _ := ret[0].(mount.Reader)
+	ret1, _ := ret[1].(error)
+	return ret0, ret1
 }
 
 // FetchUnsealedPiece indicates an expected call of FetchUnsealedPiece.
-func (mr *MockMinerAPIMockRecorder) FetchUnsealedPiece(arg0, arg1, arg2 interface{}) *gomock.Call {
+func (mr *MockMinerAPIMockRecorder) FetchUnsealedPiece(arg0, arg1 interface{}) *gomock.Call {
 	mr.mock.ctrl.T.Helper()
-	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "FetchUnsealedPiece", reflect.TypeOf((*MockMinerAPI)(nil).FetchUnsealedPiece), arg0, arg1, arg2)
+	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "FetchUnsealedPiece", reflect.TypeOf((*MockMinerAPI)(nil).FetchUnsealedPiece), arg0, arg1)
 }
 
 // GetUnpaddedCARSize mocks base method.
diff --git a/markets/dagstore/mount.go b/markets/dagstore/mount.go
index e4e6242d7..0ecdc9808 100644
--- a/markets/dagstore/mount.go
+++ b/markets/dagstore/mount.go
@@ -56,11 +56,7 @@ func (l *LotusMount) Deserialize(u *url.URL) error {
 }
 
 func (l *LotusMount) Fetch(ctx context.Context) (mount.Reader, error) {
-	return (&pieceReader{
-		ctx:      ctx,
-		api:      l.API,
-		pieceCid: l.PieceCid,
-	}).init()
+	return l.API.FetchUnsealedPiece(ctx, l.PieceCid)
 }
 
 func (l *LotusMount) Info() mount.Info {
diff --git a/markets/dagstore/mount_test.go b/markets/dagstore/mount_test.go
index 820058786..d6ea54964 100644
--- a/markets/dagstore/mount_test.go
+++ b/markets/dagstore/mount_test.go
@@ -2,6 +2,7 @@ package dagstore
 
 import (
 	"context"
+	"io"
 	"io/ioutil"
 	"net/url"
 	"strings"
@@ -12,8 +13,6 @@ import (
 	"github.com/stretchr/testify/require"
 
 	"github.com/filecoin-project/dagstore/mount"
-	"github.com/filecoin-project/go-state-types/abi"
-
 	mock_dagstore "github.com/filecoin-project/lotus/markets/dagstore/mocks"
 )
 
@@ -30,8 +29,28 @@ func TestLotusMount(t *testing.T) {
 	mockLotusMountAPI := mock_dagstore.NewMockMinerAPI(mockCtrl)
 
 	mockLotusMountAPI.EXPECT().IsUnsealed(gomock.Any(), cid).Return(true, nil).Times(1)
-	mockLotusMountAPI.EXPECT().FetchUnsealedPiece(gomock.Any(), cid, uint64(0)).Return(ioutil.NopCloser(strings.NewReader("testing")), abi.UnpaddedPieceSize(7), nil).Times(1)
-	mockLotusMountAPI.EXPECT().FetchUnsealedPiece(gomock.Any(), cid, uint64(0)).Return(ioutil.NopCloser(strings.NewReader("testing")), abi.UnpaddedPieceSize(7), nil).Times(1)
+
+	mr1 := struct {
+		io.ReadCloser
+		io.ReaderAt
+		io.Seeker
+	}{
+		ReadCloser: ioutil.NopCloser(strings.NewReader("testing")),
+		ReaderAt:   nil,
+		Seeker:     nil,
+	}
+	mr2 := struct {
+		io.ReadCloser
+		io.ReaderAt
+		io.Seeker
+	}{
+		ReadCloser: ioutil.NopCloser(strings.NewReader("testing")),
+		ReaderAt:   nil,
+		Seeker:     nil,
+	}
+
+	mockLotusMountAPI.EXPECT().FetchUnsealedPiece(gomock.Any(), cid).Return(mr1, nil).Times(1)
+	mockLotusMountAPI.EXPECT().FetchUnsealedPiece(gomock.Any(), cid).Return(mr2, nil).Times(1)
 	mockLotusMountAPI.EXPECT().GetUnpaddedCARSize(ctx, cid).Return(uint64(100), nil).Times(1)
 
 	mnt, err := NewLotusMount(cid, mockLotusMountAPI)
diff --git a/markets/dagstore/wrapper_migration_test.go b/markets/dagstore/wrapper_migration_test.go
index 502105499..e46f8779b 100644
--- a/markets/dagstore/wrapper_migration_test.go
+++ b/markets/dagstore/wrapper_migration_test.go
@@ -6,9 +6,9 @@ import (
 	"testing"
 
 	"github.com/stretchr/testify/require"
-	"golang.org/x/xerrors"
 
 	"github.com/filecoin-project/dagstore"
+	"github.com/filecoin-project/dagstore/mount"
 	"github.com/filecoin-project/go-state-types/abi"
 
 	"github.com/filecoin-project/go-fil-markets/retrievalmarket"
@@ -127,17 +127,20 @@ type wrappedSA struct {
 	retrievalmarket.SectorAccessor
 }
 
-func (w *wrappedSA) UnsealSectorAt(ctx context.Context, sectorID abi.SectorNumber, pieceOffset abi.UnpaddedPieceSize, startOffset uint64, length abi.UnpaddedPieceSize) (io.ReadCloser, error) {
+func (w *wrappedSA) UnsealSectorAt(ctx context.Context, sectorID abi.SectorNumber, pieceOffset abi.UnpaddedPieceSize, length abi.UnpaddedPieceSize) (mount.Reader, error) {
 	r, err := w.UnsealSector(ctx, sectorID, pieceOffset, length)
 	if err != nil {
 		return nil, err
 	}
-	if startOffset > 0 {
-		if _, err := io.CopyN(io.Discard, r, int64(startOffset)); err != nil {
-			return nil, xerrors.Errorf("discard start off: %w", err)
-		}
-	}
-	return r, err
+	return struct {
+		io.ReadCloser
+		io.Seeker
+		io.ReaderAt
+	}{
+		ReadCloser: r,
+		Seeker:     nil,
+		ReaderAt:   nil,
+	}, err
 }
 
 var _ SectorAccessor = &wrappedSA{}
diff --git a/markets/dagstore/wrapper_test.go b/markets/dagstore/wrapper_test.go
index a4a6215e1..48e01100b 100644
--- a/markets/dagstore/wrapper_test.go
+++ b/markets/dagstore/wrapper_test.go
@@ -3,7 +3,6 @@ package dagstore
 import (
 	"bytes"
 	"context"
-	"io"
 	"os"
 	"testing"
 	"time"
@@ -12,8 +11,6 @@ import (
 	"github.com/stretchr/testify/require"
 	"golang.org/x/xerrors"
 
-	"github.com/filecoin-project/go-state-types/abi"
-
 	"github.com/filecoin-project/dagstore"
 	"github.com/filecoin-project/dagstore/mount"
 	"github.com/filecoin-project/dagstore/shard"
@@ -192,7 +189,7 @@ func (m mockLotusMount) Start(ctx context.Context) error {
 	return nil
 }
 
-func (m mockLotusMount) FetchUnsealedPiece(ctx context.Context, pieceCid cid.Cid, offset uint64) (io.ReadCloser, abi.UnpaddedPieceSize, error) {
+func (m mockLotusMount) FetchUnsealedPiece(context.Context, cid.Cid) (mount.Reader, error) {
 	panic("implement me")
 }
 
diff --git a/markets/sectoraccessor/sectoraccessor.go b/markets/sectoraccessor/sectoraccessor.go
index f70aca103..4320e3fb1 100644
--- a/markets/sectoraccessor/sectoraccessor.go
+++ b/markets/sectoraccessor/sectoraccessor.go
@@ -4,8 +4,16 @@ import (
 	"context"
 	"io"
 
+	"github.com/ipfs/go-cid"
+	logging "github.com/ipfs/go-log/v2"
 	"golang.org/x/xerrors"
 
+	"github.com/filecoin-project/dagstore/mount"
+	"github.com/filecoin-project/go-address"
+	"github.com/filecoin-project/go-fil-markets/retrievalmarket"
+	"github.com/filecoin-project/go-state-types/abi"
+	specstorage "github.com/filecoin-project/specs-storage/storage"
+
 	"github.com/filecoin-project/lotus/api"
 	"github.com/filecoin-project/lotus/api/v1api"
 	"github.com/filecoin-project/lotus/chain/types"
@@ -14,14 +22,6 @@ import (
 	"github.com/filecoin-project/lotus/markets/dagstore"
 	"github.com/filecoin-project/lotus/node/modules/dtypes"
 	"github.com/filecoin-project/lotus/storage/sectorblocks"
-
-	"github.com/filecoin-project/go-address"
-	"github.com/filecoin-project/go-fil-markets/retrievalmarket"
-	"github.com/filecoin-project/go-state-types/abi"
-	specstorage "github.com/filecoin-project/specs-storage/storage"
-
-	"github.com/ipfs/go-cid"
-	logging "github.com/ipfs/go-log/v2"
 )
 
 var log = logging.Logger("sectoraccessor")
@@ -40,10 +40,10 @@ func NewSectorAccessor(maddr dtypes.MinerAddress, secb sectorblocks.SectorBuilde
 }
 
 func (sa *sectorAccessor) UnsealSector(ctx context.Context, sectorID abi.SectorNumber, pieceOffset abi.UnpaddedPieceSize, length abi.UnpaddedPieceSize) (io.ReadCloser, error) {
-	return sa.UnsealSectorAt(ctx, sectorID, pieceOffset, 0, length)
+	return sa.UnsealSectorAt(ctx, sectorID, pieceOffset, length)
 }
 
-func (sa *sectorAccessor) UnsealSectorAt(ctx context.Context, sectorID abi.SectorNumber, pieceOffset abi.UnpaddedPieceSize, startOffset uint64, length abi.UnpaddedPieceSize) (io.ReadCloser, error) {
+func (sa *sectorAccessor) UnsealSectorAt(ctx context.Context, sectorID abi.SectorNumber, pieceOffset abi.UnpaddedPieceSize, length abi.UnpaddedPieceSize) (mount.Reader, error) {
 	log.Debugf("get sector %d, pieceOffset %d, length %d", sectorID, pieceOffset, length)
 	si, err := sa.sectorsStatus(ctx, sectorID, false)
 	if err != nil {
@@ -69,8 +69,8 @@ func (sa *sectorAccessor) UnsealSectorAt(ctx context.Context, sectorID abi.Secto
 	}
 
 	// Get a reader for the piece, unsealing the piece if necessary
-	log.Debugf("read piece in sector %d, pieceOffset %d, startOffset %d, length %d from miner %d", sectorID, pieceOffset, startOffset, length, mid)
-	r, unsealed, err := sa.pp.ReadPiece(ctx, ref, storiface.UnpaddedByteIndex(pieceOffset), startOffset, length, si.Ticket.Value, commD)
+	log.Debugf("read piece in sector %d, pieceOffset %d, length %d from miner %d", sectorID, pieceOffset, length, mid)
+	r, unsealed, err := sa.pp.ReadPiece(ctx, ref, storiface.UnpaddedByteIndex(pieceOffset), length, si.Ticket.Value, commD)
 	if err != nil {
 		return nil, xerrors.Errorf("failed to unseal piece from sector %d: %w", sectorID, err)
 	}