move to the empty nodes first

weed/shell/command_volume_balance.go

@@ -213,6 +213,16 @@ func capacityByMaxVolumeCount(diskType types.DiskType) CapacityFunc {
 	}
 }
 
+func capacityByFreeVolumeCount(diskType types.DiskType) CapacityFunc {
+	return func(info *master_pb.DataNodeInfo) int {
+		diskInfo, found := info.DiskInfos[string(diskType)]
+		if !found {
+			return 0
+		}
+		return int(diskInfo.MaxVolumeCount - diskInfo.VolumeCount)
+	}
+}
+
 func (n *Node) localVolumeRatio(capacityFunc CapacityFunc) float64 {
 	return divide(len(n.selectedVolumes), capacityFunc(n.info))
 }

weed/shell/command_volume_server_evacuate.go

@@ -180,7 +180,7 @@ func moveAwayOneEcVolume(commandEnv *CommandEnv, ecShardInfo *master_pb.VolumeEc
 
 func moveAwayOneNormalVolume(commandEnv *CommandEnv, volumeReplicas map[uint32][]*VolumeReplica, vol *master_pb.VolumeInformationMessage, thisNode *Node, otherNodes []*Node, applyChange bool) (hasMoved bool, err error) {
 	sort.Slice(otherNodes, func(i, j int) bool {
-		return otherNodes[i].localVolumeRatio(capacityByMaxVolumeCount(types.ToDiskType(vol.DiskType))) < otherNodes[j].localVolumeRatio(capacityByMaxVolumeCount(types.ToDiskType(vol.DiskType)))
+		return otherNodes[i].localVolumeRatio(capacityByFreeVolumeCount(types.ToDiskType(vol.DiskType))) > otherNodes[j].localVolumeRatio(capacityByFreeVolumeCount(types.ToDiskType(vol.DiskType)))
 	})
 
 	for i := 0; i < len(otherNodes); i++ {