Improve EC shards balancing logic regarding replica placement settings.

The replica placement type specifies numebr of _replicas_ on the same/different rack;
that means we can have one EC shard copy on each, even if the replica setting is zero.

This PR reworks replica placement parsing for EC rebalancing, so we check allow
(replica placement + 1) when selecting racks and nodes to balance EC shards into.

weed/shell/command_ec_common.go

@@ -783,8 +783,8 @@ func (ecb *ecBalancer) pickRackToBalanceShardsInto(rackToEcNodes map[RackId]*EcR
 			details += fmt.Sprintf("  Skipped %s because it has no free slots\n", rackId)
 			continue
 		}
-		if ecb.replicaPlacement != nil && shards >= ecb.replicaPlacement.DiffRackCount {
-			details += fmt.Sprintf("  Skipped %s because shards %d >= replica placement limit for other racks (%d)\n", rackId, shards, ecb.replicaPlacement.DiffRackCount)
+		if ecb.replicaPlacement != nil && shards > ecb.replicaPlacement.DiffRackCount {
+			details += fmt.Sprintf("  Skipped %s because shards %d > replica placement limit for other racks (%d)\n", rackId, shards, ecb.replicaPlacement.DiffRackCount)
 			continue
 		}
 
@@ -977,8 +977,8 @@ func (ecb *ecBalancer) pickEcNodeToBalanceShardsInto(vid needle.VolumeId, existi
 		}
 
 		shards := nodeShards[node]
-		if ecb.replicaPlacement != nil && shards >= ecb.replicaPlacement.SameRackCount {
-			details += fmt.Sprintf("  Skipped %s because shards %d >= replica placement limit for the rack (%d)\n", node.info.Id, shards, ecb.replicaPlacement.SameRackCount)
+		if ecb.replicaPlacement != nil && shards > ecb.replicaPlacement.SameRackCount {
+			details += fmt.Sprintf("  Skipped %s because shards %d > replica placement limit for the rack (%d)\n", node.info.Id, shards, ecb.replicaPlacement.SameRackCount)
 			continue
 		}
 

weed/shell/command_ec_common_test.go

@@ -138,8 +138,8 @@ func TestPickRackToBalanceShardsInto(t *testing.T) {
 		{topologyEc, "6241", "123", []string{"rack1", "rack2", "rack3", "rack4", "rack5", "rack6"}, ""},
 		{topologyEc, "6242", "123", []string{"rack1", "rack2", "rack3", "rack4", "rack5", "rack6"}, ""},
 		// EC volumes.
-		{topologyEc, "9577", "", nil, "shards 1 >= replica placement limit for other racks (0)"},
-		{topologyEc, "9577", "111", nil, "shards 1 >= replica placement limit for other racks (1)"},
+		{topologyEc, "9577", "", nil, "shards 1 > replica placement limit for other racks (0)"},
+		{topologyEc, "9577", "111", []string{"rack1", "rack2", "rack3"}, ""},
 		{topologyEc, "9577", "222", []string{"rack1", "rack2", "rack3"}, ""},
 		{topologyEc, "10457", "222", []string{"rack1"}, ""},
 		{topologyEc, "12737", "222", []string{"rack2"}, ""},