diff --git a/weed/placement/placement.go b/weed/placement/placement.go
index 274fb3e13..29f333cc8 100644
--- a/weed/placement/placement.go
+++ b/weed/placement/placement.go
@@ -20,6 +20,12 @@ type PlacementPreference struct {
 	// Exclude names nodes already spoken for by the same plan, so a caller
 	// placing several copies does not stack them on one node.
 	Exclude map[string]bool
+	// Accept rejects candidates the caller cannot use for reasons placement does
+	// not model -- replica placement rules, a node already holding the volume.
+	// It receives the candidate's rack and data center because the constraints
+	// that need them are exactly the ones a bare node cannot express. Nil
+	// accepts everything.
+	Accept func(node *master_pb.DataNodeInfo, dataCenter, rack string) bool
 	// VolumeBytes is what this move will actually consume on the destination.
 	// Zero falls back to the tier's average volume size, which is all a caller
 	// planning a not-yet-created volume can know.
@@ -73,6 +79,9 @@ func PickTarget(topo *master_pb.TopologyInfo, pref PlacementPreference) *master_
 		if d == nil || d.VolumeCount >= d.MaxVolumeCount {
 			continue
 		}
+		if pref.Accept != nil && !pref.Accept(n.info, n.dc, n.rack) {
+			continue
+		}
 		c := candidate{node: n}
 		c.bytes, c.hasBytes = d.DiskFreeBytes, d.DiskTotalBytes != 0
 		c.slots = d.MaxVolumeCount - d.VolumeCount
diff --git a/weed/placement/placement_test.go b/weed/placement/placement_test.go
index f36faa8fc..1b553bc87 100644
--- a/weed/placement/placement_test.go
+++ b/weed/placement/placement_test.go
@@ -224,3 +224,35 @@ func TestPickTargetReservesTheVolumeSize(t *testing.T) {
 		t.Fatalf("second pick %q, want a2 after 800 bytes were spent on a1", second.GetId())
 	}
 }
+
+func TestPickTargetHonoursTheCallerPredicate(t *testing.T) {
+	// Constraints placement does not model -- replica placement, a node already
+	// holding the volume -- stay with the caller, which keeps them out of the
+	// ranking rather than duplicating them here.
+	topo := placementTopo(
+		placementNode("a1", 10, 1, 1000, 900),
+		placementNode("a2", 10, 1, 1000, 500),
+	)
+	got := PickTarget(topo, PlacementPreference{
+		Source: "z9", DiskType: types.SsdType,
+		Accept: func(n *master_pb.DataNodeInfo, dc, rack string) bool { return n.Id != "a1" },
+	})
+	if got.GetId() != "a2" {
+		t.Fatalf("got %q, want a2 -- a1 was rejected despite being emptier", got.GetId())
+	}
+}
+
+func TestPickTargetPredicateSeesRackAndDataCenter(t *testing.T) {
+	topo := placementTopo(placementNode("a1", 10, 1, 1000, 900))
+	var sawDc, sawRack string
+	PickTarget(topo, PlacementPreference{
+		Source: "z9", DiskType: types.SsdType,
+		Accept: func(n *master_pb.DataNodeInfo, dc, rack string) bool {
+			sawDc, sawRack = dc, rack
+			return true
+		},
+	})
+	if sawDc != "dc1" || sawRack != "a" {
+		t.Fatalf("predicate saw dc=%q rack=%q, want dc1/a", sawDc, sawRack)
+	}
+}