diff --git a/pkg/storage/drivers/fs/fs_multipart.go b/pkg/storage/drivers/fs/fs_multipart.go
index 779787504..e2f89878a 100644
--- a/pkg/storage/drivers/fs/fs_multipart.go
+++ b/pkg/storage/drivers/fs/fs_multipart.go
@@ -36,6 +36,69 @@ type Multiparts struct {
 	ActiveSession map[string]*MultipartSession
 }
 
+func (fs *fsDriver) loadActiveSessions(bucket string) {
+	bucketPath := path.Join(fs.root, bucket)
+	_, err := os.Stat(bucketPath)
+	if err != nil {
+		return
+	}
+	activeSessionFile, err := os.OpenFile(bucketPath+"$activeSession", os.O_RDONLY, 0600)
+	if err != nil {
+		return
+	}
+	defer activeSessionFile.Close()
+	var deserializedActiveSession map[string]*MultipartSession
+	decoder := json.NewDecoder(activeSessionFile)
+	err = decoder.Decode(&deserializedActiveSession)
+	if err != nil {
+		return
+	}
+	for key, value := range deserializedActiveSession {
+		fs.multiparts.ActiveSession[key] = value
+	}
+	return
+}
+
+func (fs *fsDriver) isValidUploadID(key, uploadID string) bool {
+	s, ok := fs.multiparts.ActiveSession[key]
+	if !ok {
+		return false
+	}
+	if uploadID == s.UploadID {
+		return true
+	}
+	return false
+}
+
+func (fs *fsDriver) writePart(objectPath string, partID int, size int64, data io.Reader) (drivers.PartMetadata, error) {
+	partPath := objectPath + fmt.Sprintf("$%d", partID)
+	// write part
+	partFile, err := os.OpenFile(partPath, os.O_WRONLY|os.O_CREATE, 0600)
+	if err != nil {
+		return drivers.PartMetadata{}, iodine.New(err, nil)
+	}
+	defer partFile.Close()
+
+	h := md5.New()
+	mw := io.MultiWriter(partFile, h)
+
+	_, err = io.CopyN(mw, data, size)
+	if err != nil {
+		return drivers.PartMetadata{}, iodine.New(err, nil)
+	}
+
+	fi, err := os.Stat(partPath)
+	if err != nil {
+		return drivers.PartMetadata{}, iodine.New(err, nil)
+	}
+	partMetadata := drivers.PartMetadata{}
+	partMetadata.ETag = hex.EncodeToString(h.Sum(nil))
+	partMetadata.PartNumber = partID
+	partMetadata.Size = fi.Size()
+	partMetadata.LastModified = fi.ModTime()
+	return partMetadata, nil
+}
+
 // byKey is a sortable interface for UploadMetadata slice
 type byKey []*drivers.UploadMetadata
 
@@ -51,7 +114,6 @@ func (fs *fsDriver) ListMultipartUploads(bucket string, resources drivers.Bucket
 	}
 	bucketPath := path.Join(fs.root, bucket)
 	_, err := os.Stat(bucketPath)
-
 	// check bucket exists
 	if os.IsNotExist(err) {
 		return drivers.BucketMultipartResourcesMetadata{}, iodine.New(drivers.BucketNotFound{Bucket: bucket}, nil)
@@ -59,27 +121,11 @@ func (fs *fsDriver) ListMultipartUploads(bucket string, resources drivers.Bucket
 	if err != nil {
 		return drivers.BucketMultipartResourcesMetadata{}, iodine.New(drivers.InternalError{}, nil)
 	}
+	// load from disk
+	fs.loadActiveSessions(bucket)
 
-	if _, err := os.Stat(bucketPath + "$activeSession"); os.IsNotExist(err) {
-		return drivers.BucketMultipartResourcesMetadata{}, nil
-	}
-	if err != nil {
-		return drivers.BucketMultipartResourcesMetadata{}, iodine.New(err, nil)
-	}
-	activeSessionFile, err := os.OpenFile(bucketPath+"$activeSession", os.O_RDONLY, 0600)
-	if err != nil {
-		return drivers.BucketMultipartResourcesMetadata{}, iodine.New(err, nil)
-	}
-	defer activeSessionFile.Close()
-
-	var deserializedActiveSession map[string]*MultipartSession
-	decoder := json.NewDecoder(activeSessionFile)
-	err = decoder.Decode(&deserializedActiveSession)
-	if err != nil {
-		return drivers.BucketMultipartResourcesMetadata{}, iodine.New(err, nil)
-	}
 	var uploads []*drivers.UploadMetadata
-	for key, session := range deserializedActiveSession {
+	for key, session := range fs.multiparts.ActiveSession {
 		if strings.HasPrefix(key, resources.Prefix) {
 			if len(uploads) > resources.MaxUploads {
 				sort.Sort(byKey(uploads))
@@ -123,6 +169,34 @@ func (fs *fsDriver) ListMultipartUploads(bucket string, resources drivers.Bucket
 	return resources, nil
 }
 
+func (fs *fsDriver) concatParts(parts map[int]string, objectPath string, mw io.Writer) error {
+	for i := 1; i <= len(parts); i++ {
+		recvMD5 := parts[i]
+		partFile, err := os.OpenFile(objectPath+fmt.Sprintf("$%d", i), os.O_RDONLY, 0600)
+		if err != nil {
+			return iodine.New(err, nil)
+		}
+		obj, err := ioutil.ReadAll(partFile)
+		if err != nil {
+			return iodine.New(err, nil)
+		}
+		calcMD5Bytes := md5.Sum(obj)
+		// complete multi part request header md5sum per part is hex encoded
+		recvMD5Bytes, err := hex.DecodeString(strings.Trim(recvMD5, "\""))
+		if err != nil {
+			return iodine.New(drivers.InvalidDigest{Md5: recvMD5}, nil)
+		}
+		if !bytes.Equal(recvMD5Bytes, calcMD5Bytes[:]) {
+			return iodine.New(drivers.BadDigest{Md5: recvMD5}, nil)
+		}
+		_, err = io.Copy(mw, bytes.NewBuffer(obj))
+		if err != nil {
+			return iodine.New(err, nil)
+		}
+	}
+	return nil
+}
+
 func (fs *fsDriver) NewMultipartUpload(bucket, key, contentType string) (string, error) {
 	fs.lock.Lock()
 	defer fs.lock.Unlock()
@@ -160,13 +234,15 @@ func (fs *fsDriver) NewMultipartUpload(bucket, key, contentType string) (string,
 	}
 
 	var activeSessionFile *os.File
-	if _, err := os.Stat(bucketPath + "$activeSession"); os.IsNotExist(err) {
+	_, err = os.Stat(bucketPath + "$activeSession")
+	switch {
+	case os.IsNotExist(err):
 		activeSessionFile, err = os.OpenFile(bucketPath+"$activeSession", os.O_WRONLY|os.O_CREATE, 0600)
 		if err != nil {
 			return "", iodine.New(err, nil)
 		}
-	} else {
-		activeSessionFile, err = os.OpenFile(bucketPath+"$activeSession", os.O_WRONLY, 0600)
+	default:
+		activeSessionFile, err = os.OpenFile(bucketPath+"$activeSession", os.O_WRONLY|os.O_APPEND, 0600)
 		if err != nil {
 			return "", iodine.New(err, nil)
 		}
@@ -177,11 +253,11 @@ func (fs *fsDriver) NewMultipartUpload(bucket, key, contentType string) (string,
 	uploadIDSum := sha512.Sum512(id)
 	uploadID := base64.URLEncoding.EncodeToString(uploadIDSum[:])[:47]
 
-	file, err := os.OpenFile(objectPath+"$multiparts", os.O_WRONLY|os.O_CREATE, 0600)
+	multiPartfile, err := os.OpenFile(objectPath+"$multiparts", os.O_WRONLY|os.O_CREATE, 0600)
 	if err != nil {
 		return "", iodine.New(err, nil)
 	}
-	defer file.Close()
+	defer multiPartfile.Close()
 
 	mpartSession := new(MultipartSession)
 	mpartSession.TotalParts = 0
@@ -191,7 +267,7 @@ func (fs *fsDriver) NewMultipartUpload(bucket, key, contentType string) (string,
 	mpartSession.Parts = parts
 	fs.multiparts.ActiveSession[key] = mpartSession
 
-	encoder := json.NewEncoder(file)
+	encoder := json.NewEncoder(multiPartfile)
 	err = encoder.Encode(mpartSession)
 	if err != nil {
 		return "", iodine.New(err, nil)
@@ -205,46 +281,6 @@ func (fs *fsDriver) NewMultipartUpload(bucket, key, contentType string) (string,
 	return uploadID, nil
 }
 
-func (fs *fsDriver) isValidUploadID(key, uploadID string) bool {
-	s, ok := fs.multiparts.ActiveSession[key]
-	if !ok {
-		return false
-	}
-	if uploadID == s.UploadID {
-		return true
-	}
-	return false
-}
-
-func (fs *fsDriver) writePart(objectPath string, partID int, size int64, data io.Reader) (drivers.PartMetadata, error) {
-	partPath := objectPath + fmt.Sprintf("$%d", partID)
-	// write part
-	partFile, err := os.OpenFile(partPath, os.O_WRONLY|os.O_CREATE, 0600)
-	if err != nil {
-		return drivers.PartMetadata{}, iodine.New(err, nil)
-	}
-	defer partFile.Close()
-
-	h := md5.New()
-	mw := io.MultiWriter(partFile, h)
-
-	_, err = io.CopyN(mw, data, size)
-	if err != nil {
-		return drivers.PartMetadata{}, iodine.New(err, nil)
-	}
-
-	fi, err := os.Stat(partPath)
-	if err != nil {
-		return drivers.PartMetadata{}, iodine.New(err, nil)
-	}
-	partMetadata := drivers.PartMetadata{}
-	partMetadata.ETag = hex.EncodeToString(h.Sum(nil))
-	partMetadata.PartNumber = partID
-	partMetadata.Size = fi.Size()
-	partMetadata.LastModified = fi.ModTime()
-	return partMetadata, nil
-}
-
 // partNumber is a sortable interface for Part slice
 type partNumber []*drivers.PartMetadata
 
@@ -321,7 +357,7 @@ func (fs *fsDriver) CreateObjectPart(bucket, key, uploadID string, partID int, c
 		}
 	}
 
-	multiPartfile, err := os.OpenFile(objectPath+"$multiparts", os.O_RDWR, 0600)
+	multiPartfile, err := os.OpenFile(objectPath+"$multiparts", os.O_RDWR|os.O_APPEND, 0600)
 	if err != nil {
 		return "", iodine.New(err, nil)
 	}
@@ -346,34 +382,6 @@ func (fs *fsDriver) CreateObjectPart(bucket, key, uploadID string, partID int, c
 	return partMetadata.ETag, nil
 }
 
-func (fs *fsDriver) concatParts(parts map[int]string, objectPath string, mw io.Writer) error {
-	for i := 1; i <= len(parts); i++ {
-		recvMD5 := parts[i]
-		partFile, err := os.OpenFile(objectPath+fmt.Sprintf("$%d", i), os.O_RDONLY, 0600)
-		if err != nil {
-			return iodine.New(err, nil)
-		}
-		obj, err := ioutil.ReadAll(partFile)
-		if err != nil {
-			return iodine.New(err, nil)
-		}
-		calcMD5Bytes := md5.Sum(obj)
-		// complete multi part request header md5sum per part is hex encoded
-		recvMD5Bytes, err := hex.DecodeString(strings.Trim(recvMD5, "\""))
-		if err != nil {
-			return iodine.New(drivers.InvalidDigest{Md5: recvMD5}, nil)
-		}
-		if !bytes.Equal(recvMD5Bytes, calcMD5Bytes[:]) {
-			return iodine.New(drivers.BadDigest{Md5: recvMD5}, nil)
-		}
-		_, err = io.Copy(mw, bytes.NewBuffer(obj))
-		if err != nil {
-			return iodine.New(err, nil)
-		}
-	}
-	return nil
-}
-
 func (fs *fsDriver) CompleteMultipartUpload(bucket, key, uploadID string, parts map[int]string) (string, error) {
 	fs.lock.Lock()
 	defer fs.lock.Unlock()
@@ -470,6 +478,9 @@ func (fs *fsDriver) ListObjectParts(bucket, key string, resources drivers.Object
 	fs.lock.Lock()
 	defer fs.lock.Unlock()
 
+	// load from disk
+	fs.loadActiveSessions(bucket)
+
 	// check bucket name valid
 	if drivers.IsValidBucket(bucket) == false {
 		return drivers.ObjectResourcesMetadata{}, iodine.New(drivers.BucketNameInvalid{Bucket: bucket}, nil)
@@ -506,7 +517,7 @@ func (fs *fsDriver) ListObjectParts(bucket, key string, resources drivers.Object
 	}
 
 	objectPath := path.Join(bucketPath, key)
-	multiPartfile, err := os.OpenFile(objectPath+"$multiparts", os.O_RDWR, 0600)
+	multiPartfile, err := os.OpenFile(objectPath+"$multiparts", os.O_RDONLY, 0600)
 	if err != nil {
 		return drivers.ObjectResourcesMetadata{}, iodine.New(err, nil)
 	}