diff --git a/internal/partedio/nwriter.go b/internal/partedio/nwriter.go
index 57971bc..080b496 100644
--- a/internal/partedio/nwriter.go
+++ b/internal/partedio/nwriter.go
@@ -38,7 +38,8 @@ func NewNWriter(partSize int64, concurrency int, handler PartHandler) (io.WriteC
 	initOnce.Do(func() {
 		pool = &sync.Pool{
 			New: func() interface{} {
-				return make([]byte, partSize)
+				buf := make([]byte, partSize)
+				return &buf
 			},
 		}
 	})
@@ -87,8 +88,9 @@ func (nw *NWriter) startWriting(src io.Reader) {
 		go func() {
 			defer nw.wg.Done()
 
-			buffer := pool.Get().([]byte)
-			defer pool.Put(buffer)
+			bufferPtr := pool.Get().(*[]byte)
+			defer pool.Put(bufferPtr)
+			buffer := *bufferPtr
 
 			for nw.getErr() == nil {
 				n, err := reader.Read(buffer)
diff --git a/internal/partedio/nwriter_test.go b/internal/partedio/nwriter_test.go
index f0a1ad6..ba14395 100644
--- a/internal/partedio/nwriter_test.go
+++ b/internal/partedio/nwriter_test.go
@@ -2,7 +2,6 @@ package partedio
 
 import (
 	"errors"
-	"io"
 	"strings"
 	"sync"
 	"sync/atomic"
@@ -20,22 +19,22 @@ func TestNewNWriter(t *testing.T) {
 	}{
 		{
 			name:        "valid parameters",
-			partSize:    100,
-			handler:     func(int, int64, io.Reader) error { return nil },
+			partSize:    4,
+			handler:     func(int, int64, []byte) error { return nil },
 			concurrency: 5,
 			wantErr:     false,
 		},
 		{
 			name:        "zero part size",
 			partSize:    0,
-			handler:     func(int, int64, io.Reader) error { return nil },
+			handler:     func(int, int64, []byte) error { return nil },
 			concurrency: 5,
 			wantErr:     true,
 		},
 		{
 			name:        "negative part size",
 			partSize:    -1,
-			handler:     func(int, int64, io.Reader) error { return nil },
+			handler:     func(int, int64, []byte) error { return nil },
 			concurrency: 5,
 			wantErr:     true,
 		},
@@ -76,7 +75,7 @@ func TestNWriterWrite(t *testing.T) {
 			wantParts:   0,
 			wantErr:     false,
 			handler: func(t *testing.T) PartHandler {
-				return func(partNum int, size int64, r io.Reader) error {
+				return func(partNum int, size int64, data []byte) error {
 					t.Error("handler should not be called for empty input")
 					return nil
 				}
@@ -90,11 +89,7 @@ func TestNWriterWrite(t *testing.T) {
 			wantParts:   1,
 			wantErr:     false,
 			handler: func(t *testing.T) PartHandler {
-				return func(partNum int, size int64, r io.Reader) error {
-					data, err := io.ReadAll(r)
-					if err != nil {
-						t.Errorf("failed to read part: %v", err)
-					}
+				return func(partNum int, size int64, data []byte) error {
 					if string(data) != "test" {
 						t.Errorf("part data = %s, want %s", string(data), "test")
 					}
@@ -112,11 +107,7 @@ func TestNWriterWrite(t *testing.T) {
 			handler: func(t *testing.T) PartHandler {
 				var mu sync.Mutex
 				parts := make(map[int]string)
-				return func(partNum int, size int64, r io.Reader) error {
-					data, err := io.ReadAll(r)
-					if err != nil {
-						t.Errorf("failed to read part: %v", err)
-					}
+				return func(partNum int, size int64, data []byte) error {
 					mu.Lock()
 					parts[partNum] = string(data)
 					mu.Unlock()
@@ -132,7 +123,7 @@ func TestNWriterWrite(t *testing.T) {
 			wantParts:   1,
 			wantErr:     true,
 			handler: func(t *testing.T) PartHandler {
-				return func(partNum int, size int64, r io.Reader) error {
+				return func(partNum int, size int64, data []byte) error {
 					return errors.New("handler error")
 				}
 			},
@@ -142,9 +133,9 @@ func TestNWriterWrite(t *testing.T) {
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
 			var processedParts int64
-			handler := func(partNum int, size int64, r io.Reader) error {
+			handler := func(partNum int, size int64, data []byte) error {
 				atomic.AddInt64(&processedParts, 1)
-				return tt.handler(t)(partNum, size, r)
+				return tt.handler(t)(partNum, size, data)
 			}
 
 			w, err := NewNWriter(tt.partSize, tt.concurrency, handler)
@@ -179,7 +170,7 @@ func TestNWriterConcurrentWrites(t *testing.T) {
 	var mu sync.Mutex
 	processed := make(map[int]bool)
 
-	handler := func(partNum int, size int64, r io.Reader) error {
+	handler := func(partNum int, size int64, data []byte) error {
 		current := atomic.AddInt32(&currentConcurrent, 1)
 		defer atomic.AddInt32(&currentConcurrent, -1)