`ec.balance`: Allow EC balancing without collections. (#6488)

weed/shell/command_ec_common.go

@@ -1067,10 +1067,6 @@ func (ecb *ecBalancer) collectVolumeIdToEcNodes(collection string) map[needle.Vo
 }
 
 func EcBalance(commandEnv *CommandEnv, collections []string, dc string, ecReplicaPlacement *super_block.ReplicaPlacement, maxParallelization int, applyBalancing bool) (err error) {
-	if len(collections) == 0 {
-		return fmt.Errorf("no collections to balance")
-	}
-
 	// collect all ec nodes
 	allEcNodes, totalFreeEcSlots, err := collectEcNodesForDC(commandEnv, dc)
 	if err != nil {
@@ -1088,11 +1084,15 @@ func EcBalance(commandEnv *CommandEnv, collections []string, dc string, ecReplic
 		maxParallelization: maxParallelization,
 	}
 
+	if len(collections) == 0 {
+		fmt.Printf("WARNING: No collections to balance EC volumes across.")
+	}
 	for _, c := range collections {
 		if err = ecb.balanceEcVolumes(c); err != nil {
 			return err
 		}
 	}
+
 	if err := ecb.balanceEcRacks(); err != nil {
 		return fmt.Errorf("balance ec racks: %v", err)
 	}