diff --git a/internal/unifiedresources/metrics_targets.go b/internal/unifiedresources/metrics_targets.go
index 5865ccc48..96bc3341a 100644
--- a/internal/unifiedresources/metrics_targets.go
+++ b/internal/unifiedresources/metrics_targets.go
@@ -98,6 +98,18 @@ func BuildMetricsTarget(resource Resource, sourceTargets []SourceTarget) *Metric
 			return &MetricsTarget{ResourceType: "storage", ResourceID: st.SourceID}
 		}
 	case ResourceTypePhysicalDisk:
+		// The agent source must win over platform sources for physical
+		// disks: SMART/temperature metrics are written by the host agent
+		// under the agent's disk source ID (HostSMARTDiskSourceID in
+		// monitor_agents.go). Proxmox API does not expose detailed SMART
+		// data, so preferring its source ID here would point store readers
+		// at a key nothing writes and disk metrics would appear empty
+		// (GitHub issue #1487).
+		if st, ok := bySource[SourceAgent]; ok {
+			if resourceID := PhysicalDiskMetaMetricID(resource.PhysicalDisk, st.SourceID); resourceID != "" {
+				return &MetricsTarget{ResourceType: "disk", ResourceID: resourceID}
+			}
+		}
 		if st, ok := bySource[SourceProxmox]; ok {
 			if resourceID := PhysicalDiskMetaMetricID(resource.PhysicalDisk, st.SourceID); resourceID != "" {
 				return &MetricsTarget{ResourceType: "disk", ResourceID: resourceID}
@@ -108,11 +120,6 @@ func BuildMetricsTarget(resource Resource, sourceTargets []SourceTarget) *Metric
 				return &MetricsTarget{ResourceType: "disk", ResourceID: resourceID}
 			}
 		}
-		if st, ok := bySource[SourceAgent]; ok {
-			if resourceID := PhysicalDiskMetaMetricID(resource.PhysicalDisk, st.SourceID); resourceID != "" {
-				return &MetricsTarget{ResourceType: "disk", ResourceID: resourceID}
-			}
-		}
 	case ResourceTypePod:
 		if st, ok := bySource[SourceK8s]; ok {
 			if resourceID := CanonicalKubernetesPodMetricID(st.SourceID); resourceID != "" {
diff --git a/internal/unifiedresources/metrics_targets_test.go b/internal/unifiedresources/metrics_targets_test.go
index 16af9e1ad..f21e97fb2 100644
--- a/internal/unifiedresources/metrics_targets_test.go
+++ b/internal/unifiedresources/metrics_targets_test.go
@@ -372,6 +372,59 @@ func TestBuildMetricsTarget_UsesCanonicalPhysicalDiskMetricIDForTrueNAS(t *testi
 	}
 }
 
+func TestBuildMetricsTarget_AgentSourceWinsForPhysicalDiskMetrics(t *testing.T) {
+	// When a Proxmox node has an agent, the agent writes SMART/temperature
+	// metrics under its own disk source ID. The metrics target must resolve
+	// to the agent source ID, not the Proxmox source ID, or store readers
+	// query a key nothing writes and disk metrics appear empty (#1487).
+	// Without a serial, the source-specific fallback ID differs between
+	// sources, so source priority determines which key is returned.
+	target := BuildMetricsTarget(
+		Resource{
+			Type: ResourceTypePhysicalDisk,
+			PhysicalDisk: &PhysicalDiskMeta{
+				DiskType: "nvme",
+			},
+		},
+		[]SourceTarget{
+			{Source: SourceProxmox, SourceID: "pve-node:nvme0n1"},
+			{Source: SourceAgent, SourceID: "agent-uuid:nvme0n1"},
+		},
+	)
+	if target == nil {
+		t.Fatal("BuildMetricsTarget() returned nil")
+	}
+	if target.ResourceType != "disk" {
+		t.Fatalf("ResourceType = %q, want disk", target.ResourceType)
+	}
+	if target.ResourceID != "agent-uuid:nvme0n1" {
+		t.Fatalf("ResourceID = %q, want agent-uuid:nvme0n1 (agent source must win for physical disk SMART metrics)", target.ResourceID)
+	}
+}
+
+func TestBuildMetricsTarget_PhysicalDiskSerialWinsOverAllSources(t *testing.T) {
+	// When the disk has a serial number, it becomes the metric ID
+	// regardless of source, so the priority order doesn't matter.
+	target := BuildMetricsTarget(
+		Resource{
+			Type: ResourceTypePhysicalDisk,
+			PhysicalDisk: &PhysicalDiskMeta{
+				Serial: "SAMSUNG-SSD-870-500GB",
+			},
+		},
+		[]SourceTarget{
+			{Source: SourceProxmox, SourceID: "pve-node:sda"},
+			{Source: SourceAgent, SourceID: "agent-uuid:sda"},
+		},
+	)
+	if target == nil {
+		t.Fatal("BuildMetricsTarget() returned nil")
+	}
+	if target.ResourceID != "SAMSUNG-SSD-870-500GB" {
+		t.Fatalf("ResourceID = %q, want SAMSUNG-SSD-870-500GB (serial should be used as canonical ID)", target.ResourceID)
+	}
+}
+
 func TestBuildMetricsTarget_UsesCanonicalAppMetricIDForTrueNAS(t *testing.T) {
 	target := BuildMetricsTarget(
 		Resource{