diff --git a/weed/filesys/dirty_pages.go b/weed/filesys/dirty_pages.go
new file mode 100644
index 000000000..c056a09ba
--- /dev/null
+++ b/weed/filesys/dirty_pages.go
@@ -0,0 +1,8 @@
+package filesys
+
+type DirtyPages interface {
+	AddPage(offset int64, data []byte)
+	FlushData() error
+	ReadDirtyDataAt(data []byte, startOffset int64) (maxStop int64)
+	GetStorageOptions() (collection, replication string)
+}
diff --git a/weed/filesys/dirty_page.go b/weed/filesys/dirty_pages_continuous.go
similarity index 97%
rename from weed/filesys/dirty_page.go
rename to weed/filesys/dirty_pages_continuous.go
index 25f1d31c2..b4ec88c21 100644
--- a/weed/filesys/dirty_page.go
+++ b/weed/filesys/dirty_pages_continuous.go
@@ -22,7 +22,7 @@ type ContinuousDirtyPages struct {
 	replication    string
 }
 
-func newDirtyPages(file *File, writeOnly bool) *ContinuousDirtyPages {
+func newContinuousDirtyPages(file *File, writeOnly bool) *ContinuousDirtyPages {
 	dirtyPages := &ContinuousDirtyPages{
 		intervals: &ContinuousIntervals{},
 		f:         file,
diff --git a/weed/filesys/filehandle.go b/weed/filesys/filehandle.go
index 3ccd996ae..b23063e28 100644
--- a/weed/filesys/filehandle.go
+++ b/weed/filesys/filehandle.go
@@ -20,7 +20,7 @@ import (
 
 type FileHandle struct {
 	// cache file has been written to
-	dirtyPages     *ContinuousDirtyPages
+	dirtyPages     DirtyPages
 	entryViewCache []filer.VisibleInterval
 	reader         io.ReaderAt
 	contentType    string
@@ -38,7 +38,7 @@ type FileHandle struct {
 func newFileHandle(file *File, uid, gid uint32, writeOnly bool) *FileHandle {
 	fh := &FileHandle{
 		f:          file,
-		dirtyPages: newDirtyPages(file, writeOnly),
+		dirtyPages: newContinuousDirtyPages(file, writeOnly),
 		Uid:        uid,
 		Gid:        gid,
 	}