create new volumes on less occupied disk locations

weed/storage/disk_location.go

@@ -386,6 +386,19 @@ func (l *DiskLocation) VolumesLen() int {
 	return len(l.volumes)
 }
 
+func (l *DiskLocation) LocalVolumesLen() int {
+	l.volumesLock.RLock()
+	defer l.volumesLock.RUnlock()
+
+	count := 0
+	for _, v := range l.volumes {
+		if !v.HasRemoteFile() {
+			count++
+		}
+	}
+	return count
+}
+
 func (l *DiskLocation) SetStopping() {
 	l.volumesLock.Lock()
 	for _, v := range l.volumes {

weed/storage/store.go

@@ -165,14 +165,18 @@ func (s *Store) addVolume(vid needle.VolumeId, collection string, needleMapKind
 		return fmt.Errorf("Volume Id %d already exists!", vid)
 	}
 
-	// Find location and its index
+	// Find location with lowest local volume count (load balancing)
 	var location *DiskLocation
 	var diskId uint32
+	var minVolCount int = -1
 	for i, loc := range s.Locations {
 		if loc.DiskType == diskType && s.hasFreeDiskLocation(loc) {
-			location = loc
-			diskId = uint32(i)
-			break
+			volCount := loc.LocalVolumesLen()
+			if location == nil || volCount < minVolCount {
+				location = loc
+				diskId = uint32(i)
+				minVolCount = volCount
+			}
 		}
 	}