[volume.check.disk] was using the wrong source and target locations

fix https://github.com/chrislusf/seaweedfs/issues/2268

weed/shell/command_volume_check_disk.go

@@ -110,24 +110,24 @@ func (c *commandVolumeCheckDisk) syncTwoReplicas(aDB *needle_map.MemDb, bDB *nee
 
 		// read index db
 		if err := c.readIndexDatabase(aDB, a.info.Collection, a.info.Id, pb.NewServerAddressFromDataNode(a.location.dataNode), *verbose, writer); err != nil {
-			return err
+			return fmt.Errorf("readIndexDatabase %s volume %d: %v", a.location.dataNode, a.info.Id, err)
 		}
 		if err := c.readIndexDatabase(bDB, b.info.Collection, b.info.Id, pb.NewServerAddressFromDataNode(b.location.dataNode), *verbose, writer); err != nil {
-			return err
+			return fmt.Errorf("readIndexDatabase %s volume %d: %v", b.location.dataNode, b.info.Id, err)
 		}
 
 		// find and make up the differences
-		if aHasChanges, err = c.doVolumeCheckDisk(aDB, bDB, a, b, *verbose, writer, *applyChanges, *nonRepairThreshold); err != nil {
-			return err
+		if aHasChanges, err = c.doVolumeCheckDisk(bDB, aDB, b, a, *verbose, writer, *applyChanges, *nonRepairThreshold); err != nil {
+			return fmt.Errorf("doVolumeCheckDisk source:%s target:%s volume %d: %v", b.location.dataNode, a.location.dataNode, b.info.Id, err)
 		}
-		if bHasChanges, err = c.doVolumeCheckDisk(bDB, aDB, b, a, *verbose, writer, *applyChanges, *nonRepairThreshold); err != nil {
-			return err
+		if bHasChanges, err = c.doVolumeCheckDisk(aDB, bDB, a, b, *verbose, writer, *applyChanges, *nonRepairThreshold); err != nil {
+			return fmt.Errorf("doVolumeCheckDisk source:%s target:%s volume %d: %v", a.location.dataNode, b.location.dataNode, a.info.Id, err)
 		}
 	}
 	return nil
 }
 
-func (c *commandVolumeCheckDisk) doVolumeCheckDisk(subtrahend, minuend *needle_map.MemDb, source, target *VolumeReplica, verbose bool, writer io.Writer, applyChanges bool, nonRepairThreshold float64) (hasChanges bool, err error) {
+func (c *commandVolumeCheckDisk) doVolumeCheckDisk(minuend, subtrahend *needle_map.MemDb, source, target *VolumeReplica, verbose bool, writer io.Writer, applyChanges bool, nonRepairThreshold float64) (hasChanges bool, err error) {
 
 	// find missing keys
 	// hash join, can be more efficient