diff --git a/copy.go b/copy.go
index 158cf2e..8dab89b 100644
--- a/copy.go
+++ b/copy.go
@@ -5,6 +5,7 @@ import (
 	"errors"
 	"fmt"
 	"hash"
+	"io"
 	"os"
 	"path"
 	"sync"
@@ -12,7 +13,6 @@ import (
 	"syscall"
 	"time"
 
-	"github.com/abc950309/acp/mmap"
 	mapset "github.com/deckarep/golang-set/v2"
 	"github.com/hashicorp/go-multierror"
 	sha256 "github.com/minio/sha256-simd"
@@ -203,21 +203,18 @@ func (c *Copyer) write(ctx context.Context, job *writeJob, ch chan<- *baseJob, c
 	readErr = c.streamCopy(ctx, chans, job.src, &cntr.bytes)
 }
 
-func (c *Copyer) streamCopy(ctx context.Context, dsts []chan []byte, src *mmap.ReaderAt, bytes *int64) error {
-	if src.Len() == 0 {
-		return nil
-	}
-
+func (c *Copyer) streamCopy(ctx context.Context, dsts []chan []byte, src io.ReadCloser, bytes *int64) error {
 	for idx := int64(0); ; idx += batchSize {
-		buf, err := src.Slice(idx, batchSize)
+		buf := make([]byte, batchSize)
+
+		n, err := io.ReadFull(src, buf)
 		if err != nil {
 			return fmt.Errorf("slice mmap fail, %w", err)
 		}
 
-		copyed := make([]byte, len(buf))
-		copy(copyed, buf)
+		buf = buf[:n]
 		for _, ch := range dsts {
-			ch <- copyed
+			ch <- buf
 		}
 
 		nr := len(buf)
diff --git a/job.go b/job.go
index 71d73a6..0110197 100644
--- a/job.go
+++ b/job.go
@@ -2,11 +2,10 @@ package acp
 
 import (
 	"encoding/hex"
+	"io"
 	"io/fs"
 	"sync"
 	"time"
-
-	"github.com/abc950309/acp/mmap"
 )
 
 type jobStatus uint8
@@ -106,11 +105,11 @@ func (j *baseJob) report() *Job {
 
 type writeJob struct {
 	*baseJob
-	src *mmap.ReaderAt
+	src io.ReadCloser
 	ch  chan struct{}
 }
 
-func newWriteJob(job *baseJob, src *mmap.ReaderAt, needWait bool) *writeJob {
+func newWriteJob(job *baseJob, src io.ReadCloser, needWait bool) *writeJob {
 	j := &writeJob{
 		baseJob: job,
 		src:     src,
diff --git a/mmap/mmap_reader.go b/mmap/mmap_reader.go
new file mode 100644
index 0000000..13be2ab
--- /dev/null
+++ b/mmap/mmap_reader.go
@@ -0,0 +1,16 @@
+package mmap
+
+type Reader struct {
+	*ReaderAt
+	index int64
+}
+
+func NewReader(readerAt *ReaderAt) *Reader {
+	return &Reader{ReaderAt: readerAt}
+}
+
+func (r *Reader) Read(buf []byte) (n int, err error) {
+	n, err = r.ReadAt(buf, r.index)
+	r.index += int64(n)
+	return
+}
diff --git a/prepare.go b/prepare.go
index df3a035..c3b6790 100644
--- a/prepare.go
+++ b/prepare.go
@@ -3,6 +3,8 @@ package acp
 import (
 	"context"
 	"fmt"
+	"io"
+	"os"
 	"sync"
 
 	"github.com/abc950309/acp/mmap"
@@ -39,10 +41,36 @@ func (c *Copyer) prepare(ctx context.Context, indexed <-chan *baseJob) <-chan *w
 
 					job.setStatus(jobStatusPreparing)
 
-					file, err := mmap.Open(job.path)
+					file, err := func(path string) (io.ReadCloser, error) {
+						if c.fromDevice.linear {
+							file, err := os.Open(path)
+							if err != nil {
+								return nil, fmt.Errorf("open src file fail, %w", err)
+							}
+
+							fileInfo, err := file.Stat()
+							if err != nil {
+								return nil, fmt.Errorf("get src file stat fail, %w", err)
+							}
+							if fileInfo.Size() == 0 {
+								return nil, fmt.Errorf("get src file, size is zero")
+							}
+
+							return file, nil
+						}
+
+						readerAt, err := mmap.Open(path)
+						if err != nil {
+							return nil, fmt.Errorf("open src file by mmap fail, %w", err)
+						}
+						if readerAt.Len() == 0 {
+							return nil, fmt.Errorf("get src file by mmap, size is zero")
+						}
+
+						return mmap.NewReader(readerAt), nil
+					}(job.path)
 					if err != nil {
-						c.reportError(job.path, "", fmt.Errorf("open src file fail, %w", err))
-						return
+						c.reportError(job.path, "", err)
 					}
 
 					wj := newWriteJob(job, file, c.fromDevice.linear)