diff --git a/weed/filesys/dirty_pages_temp_file.go b/weed/filesys/dirty_pages_temp_file.go
index 9690d6768..a207eeb38 100644
--- a/weed/filesys/dirty_pages_temp_file.go
+++ b/weed/filesys/dirty_pages_temp_file.go
@@ -63,7 +63,7 @@ func (pages *TempFileDirtyPages) GetStorageOptions() (collection, replication st
 
 func (pages *TempFileDirtyPages) saveChunkedFileToStorage() {
 
-	pages.chunkedFile.ProcessEachInterval(func(file *os.File, logicChunkIndex int, interval *page_writer.ChunkWrittenInterval) {
+	pages.chunkedFile.ProcessEachInterval(func(file *os.File, logicChunkIndex page_writer.LogicChunkIndex, interval *page_writer.ChunkWrittenInterval) {
 		reader := page_writer.NewFileIntervalReader(pages.chunkedFile, logicChunkIndex, interval)
 		pages.saveChunkedFileIntevalToStorage(reader, int64(logicChunkIndex)*pages.chunkedFile.ChunkSize, interval.Size())
 	})
diff --git a/weed/filesys/page_writer/chunked_file_writer.go b/weed/filesys/page_writer/chunked_file_writer.go
index 9e98c6194..14c034900 100644
--- a/weed/filesys/page_writer/chunked_file_writer.go
+++ b/weed/filesys/page_writer/chunked_file_writer.go
@@ -7,11 +7,14 @@ import (
 	"sync"
 )
 
+type LogicChunkIndex int
+type ActualChunkIndex int
+
 // ChunkedFileWriter assumes the write requests will come in within chunks
 type ChunkedFileWriter struct {
 	dir                     string
 	file                    *os.File
-	logicToActualChunkIndex map[int]int
+	logicToActualChunkIndex map[LogicChunkIndex]ActualChunkIndex
 	chunkUsages             []*ChunkWrittenIntervalList
 	ChunkSize               int64
 	sync.Mutex
@@ -23,7 +26,7 @@ func NewChunkedFileWriter(dir string, chunkSize int64) *ChunkedFileWriter {
 	return &ChunkedFileWriter{
 		dir:                     dir,
 		file:                    nil,
-		logicToActualChunkIndex: make(map[int]int),
+		logicToActualChunkIndex: make(map[LogicChunkIndex]ActualChunkIndex),
 		ChunkSize:               chunkSize,
 	}
 }
@@ -78,20 +81,20 @@ func (cw *ChunkedFileWriter) ReadDataAt(p []byte, off int64) (maxStop int64) {
 }
 
 func (cw *ChunkedFileWriter) toActualWriteOffset(logicOffset int64) (actualOffset int64, chunkUsage *ChunkWrittenIntervalList) {
-	logicChunkIndex := int(logicOffset / cw.ChunkSize)
+	logicChunkIndex := LogicChunkIndex(logicOffset / cw.ChunkSize)
 	offsetRemainder := logicOffset % cw.ChunkSize
 	existingActualChunkIndex, found := cw.logicToActualChunkIndex[logicChunkIndex]
 	if found {
 		return int64(existingActualChunkIndex)*cw.ChunkSize + offsetRemainder, cw.chunkUsages[existingActualChunkIndex]
 	}
-	cw.logicToActualChunkIndex[logicChunkIndex] = len(cw.chunkUsages)
+	cw.logicToActualChunkIndex[logicChunkIndex] = ActualChunkIndex(len(cw.chunkUsages))
 	chunkUsage = newChunkWrittenIntervalList()
 	cw.chunkUsages = append(cw.chunkUsages, chunkUsage)
 	return int64(len(cw.chunkUsages)-1)*cw.ChunkSize + offsetRemainder, chunkUsage
 }
 
-func (cw *ChunkedFileWriter) toActualReadOffset(logicOffset int64) (actualChunkIndex int, chunkUsage *ChunkWrittenIntervalList) {
-	logicChunkIndex := int(logicOffset / cw.ChunkSize)
+func (cw *ChunkedFileWriter) toActualReadOffset(logicOffset int64) (actualChunkIndex ActualChunkIndex, chunkUsage *ChunkWrittenIntervalList) {
+	logicChunkIndex := LogicChunkIndex(logicOffset / cw.ChunkSize)
 	existingActualChunkIndex, found := cw.logicToActualChunkIndex[logicChunkIndex]
 	if found {
 		return existingActualChunkIndex, cw.chunkUsages[existingActualChunkIndex]
@@ -99,7 +102,7 @@ func (cw *ChunkedFileWriter) toActualReadOffset(logicOffset int64) (actualChunkI
 	return 0, nil
 }
 
-func (cw *ChunkedFileWriter) ProcessEachInterval(process func(file *os.File, logicChunkIndex int, interval *ChunkWrittenInterval)) {
+func (cw *ChunkedFileWriter) ProcessEachInterval(process func(file *os.File, logicChunkIndex LogicChunkIndex, interval *ChunkWrittenInterval)) {
 	for logicChunkIndex, actualChunkIndex := range cw.logicToActualChunkIndex {
 		chunkUsage := cw.chunkUsages[actualChunkIndex]
 		for t := chunkUsage.head.next; t != chunkUsage.tail; t = t.next {
@@ -123,7 +126,7 @@ type FileIntervalReader struct {
 
 var _ = io.Reader(&FileIntervalReader{})
 
-func NewFileIntervalReader(cw *ChunkedFileWriter, logicChunkIndex int, interval *ChunkWrittenInterval) *FileIntervalReader {
+func NewFileIntervalReader(cw *ChunkedFileWriter, logicChunkIndex LogicChunkIndex, interval *ChunkWrittenInterval) *FileIntervalReader {
 	actualChunkIndex, found := cw.logicToActualChunkIndex[logicChunkIndex]
 	if !found {
 		// this should never happen