diff --git a/weed/server/qa_block_cp13_8a_test.go b/weed/server/qa_block_cp13_8a_test.go
new file mode 100644
index 000000000..7d068240e
--- /dev/null
+++ b/weed/server/qa_block_cp13_8a_test.go
@@ -0,0 +1,206 @@
+package weed_server
+
+import (
+	"bytes"
+	"context"
+"testing"
+	"time"
+
+	"github.com/seaweedfs/seaweedfs/weed/pb/master_pb"
+	"github.com/seaweedfs/seaweedfs/weed/storage/blockvol"
+)
+
+// TestCP13_8A_ReplicaReadAfterReplication verifies that data replicated to
+// a replica volume can be read back through the same BlockVol instance that
+// the iSCSI adapter uses. This is the core CP13-8A investigation test.
+//
+// If this passes: the engine + weed integration is correct, and the CP13-8
+// scenario failure is in the testrunner/cluster layer.
+// If this fails: the bug is in the VS integration (adapter wiring, flusher, etc).
+func TestCP13_8A_ReplicaReadAfterReplication(t *testing.T) {
+	s := newSoakSetup(t)
+	ctx := context.Background()
+
+	// Create a volume (RF=2 sync_all).
+	resp, err := s.ms.CreateBlockVolume(ctx, &master_pb.CreateBlockVolumeRequest{
+		Name:           "cp13-8a-read",
+		SizeBytes:      1 << 20,
+		DurabilityMode: "sync_all",
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	primaryVS := resp.VolumeServer
+	entry, _ := s.ms.blockRegistry.Lookup("cp13-8a-read")
+
+	// Deliver assignments.
+	s.bs.localServerID = primaryVS
+	s.deliver(primaryVS)
+	for _, ri := range entry.Replicas {
+		s.deliver(ri.Server)
+	}
+	time.Sleep(200 * time.Millisecond)
+
+	// Write data through the primary's BlockVol (simulating iSCSI write).
+	primaryPath := entry.Path
+	var primaryVol *blockvol.BlockVol
+	s.store.IterateBlockVolumes(func(path string, vol *blockvol.BlockVol) {
+		if path == primaryPath {
+			primaryVol = vol
+		}
+	})
+	if primaryVol == nil {
+		t.Fatal("primary volume not found in store")
+	}
+
+	// Write test pattern.
+	testData := make([]byte, 4096)
+	for i := range testData {
+		testData[i] = byte(i % 251) // distinctive non-zero pattern
+	}
+	if err := primaryVol.WriteLBA(0, testData); err != nil {
+		t.Fatalf("WriteLBA on primary: %v", err)
+	}
+	if err := primaryVol.WriteLBA(1, testData); err != nil {
+		t.Fatalf("WriteLBA on primary LBA 1: %v", err)
+	}
+
+	// SyncCache to trigger sync_all barrier (replicates + confirms durability).
+	if err := primaryVol.SyncCache(); err != nil {
+		t.Fatalf("SyncCache: %v", err)
+	}
+
+	// Now find the REPLICA volume and read from it.
+	// In the soak setup, both primary and replica are in the same store.
+	var replicaPath string
+	for _, ri := range entry.Replicas {
+		replicaPath = ri.Path
+		break
+	}
+	if replicaPath == "" {
+		t.Fatal("no replica path found")
+	}
+
+	var replicaVol *blockvol.BlockVol
+	s.store.IterateBlockVolumes(func(path string, vol *blockvol.BlockVol) {
+		if path == replicaPath {
+			replicaVol = vol
+		}
+	})
+	if replicaVol == nil {
+		t.Fatal("replica volume not found in store")
+	}
+
+	// Let flusher run on replica (same as production).
+	time.Sleep(200 * time.Millisecond)
+
+	// Read from replica — this is what the iSCSI adapter would do.
+	got, err := replicaVol.ReadLBA(0, 4096)
+	if err != nil {
+		t.Fatalf("ReadLBA on replica: %v", err)
+	}
+
+	if bytes.Equal(got, make([]byte, 4096)) {
+		t.Fatal("CP13-8A: replica ReadLBA returned all zeros — data not visible")
+	}
+
+	if !bytes.Equal(got, testData) {
+		t.Fatalf("CP13-8A: replica data mismatch at LBA 0: got[0]=%d want[0]=%d", got[0], testData[0])
+	}
+
+	// Read LBA 1 too.
+	got1, err := replicaVol.ReadLBA(1, 4096)
+	if err != nil {
+		t.Fatalf("ReadLBA on replica LBA 1: %v", err)
+	}
+	if !bytes.Equal(got1, testData) {
+		t.Fatalf("CP13-8A: replica data mismatch at LBA 1")
+	}
+
+	// Also test through the adapter path (what iSCSI actually calls).
+	adapter := blockvol.NewBlockVolAdapter(replicaVol)
+	adapterGot, err := adapter.ReadAt(0, 4096)
+	if err != nil {
+		t.Fatalf("adapter ReadAt: %v", err)
+	}
+	if !bytes.Equal(adapterGot, testData) {
+		t.Fatalf("CP13-8A: adapter data mismatch at LBA 0")
+	}
+
+	t.Log("CP13-8A: replica reads return correct data through both ReadLBA and adapter.ReadAt")
+}
+
+// TestCP13_8A_ReplicaReadAfterPromotion verifies that after promoting a
+// replica to primary, the data is still readable.
+func TestCP13_8A_ReplicaReadAfterPromotion(t *testing.T) {
+	s := newSoakSetup(t)
+	ctx := context.Background()
+
+	resp, err := s.ms.CreateBlockVolume(ctx, &master_pb.CreateBlockVolumeRequest{
+		Name:           "cp13-8a-promote",
+		SizeBytes:      1 << 20,
+		DurabilityMode: "sync_all",
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	primaryVS := resp.VolumeServer
+	entry, _ := s.ms.blockRegistry.Lookup("cp13-8a-promote")
+
+	s.bs.localServerID = primaryVS
+	s.deliver(primaryVS)
+	for _, ri := range entry.Replicas {
+		s.deliver(ri.Server)
+	}
+	time.Sleep(200 * time.Millisecond)
+
+	// Write through primary.
+	var primaryVol *blockvol.BlockVol
+	s.store.IterateBlockVolumes(func(path string, vol *blockvol.BlockVol) {
+		if path == entry.Path {
+			primaryVol = vol
+		}
+	})
+	testData := make([]byte, 4096)
+	for i := range testData {
+		testData[i] = byte((i + 37) % 251)
+	}
+	if err := primaryVol.WriteLBA(0, testData); err != nil {
+		t.Fatal(err)
+	}
+	if err := primaryVol.SyncCache(); err != nil {
+		t.Fatal(err)
+	}
+
+	// Find replica.
+	var replicaPath string
+	for _, ri := range entry.Replicas {
+		replicaPath = ri.Path
+	}
+	var replicaVol *blockvol.BlockVol
+	s.store.IterateBlockVolumes(func(path string, vol *blockvol.BlockVol) {
+		if path == replicaPath {
+			replicaVol = vol
+		}
+	})
+
+	// Promote replica to primary.
+	if err := replicaVol.HandleAssignment(2, blockvol.RolePrimary, 30*time.Second); err != nil {
+		t.Fatalf("promote replica: %v", err)
+	}
+
+	// Read after promotion (let flusher run).
+	time.Sleep(200 * time.Millisecond)
+	got, err := replicaVol.ReadLBA(0, 4096)
+	if err != nil {
+		t.Fatalf("ReadLBA after promotion: %v", err)
+	}
+	if bytes.Equal(got, make([]byte, 4096)) {
+		t.Fatal("CP13-8A: promoted replica reads zeros after promotion")
+	}
+	if !bytes.Equal(got, testData) {
+		t.Fatalf("CP13-8A: promoted replica data mismatch")
+	}
+
+	t.Log("CP13-8A: promoted replica reads correct data")
+}
diff --git a/weed/server/qa_block_soak_test.go b/weed/server/qa_block_soak_test.go
index 501abc9c9..3e873cddc 100644
--- a/weed/server/qa_block_soak_test.go
+++ b/weed/server/qa_block_soak_test.go
@@ -3,6 +3,7 @@ package weed_server
 import (
 	"context"
 	"fmt"
+	"hash/fnv"
 	"os"
 	"path/filepath"
 	"strings"
@@ -68,13 +69,20 @@ func newSoakSetup(t *testing.T) *soakSetup {
 		if idx := strings.LastIndex(server, ":"); idx >= 0 {
 			host = server[:idx]
 		}
+		// Use deterministic ports for replication (matching production ReplicationPorts behavior).
+		h := fnv.New32a()
+		h.Write([]byte(volPath))
+		offset := int(h.Sum32()%500) * 3
+		dataPort := 14000 + offset
+		ctrlPort := dataPort + 1
+		rebuildPort := dataPort + 2
 		return &blockAllocResult{
 			Path:              volPath,
 			IQN:               fmt.Sprintf("iqn.2024.test:%s", name),
 			ISCSIAddr:         host + ":3260",
-			ReplicaDataAddr:   server + ":14260",
-			ReplicaCtrlAddr:   server + ":14261",
-			RebuildListenAddr: server + ":15000",
+			ReplicaDataAddr:   fmt.Sprintf("127.0.0.1:%d", dataPort),
+			ReplicaCtrlAddr:   fmt.Sprintf("127.0.0.1:%d", ctrlPort),
+			RebuildListenAddr: fmt.Sprintf("127.0.0.1:%d", rebuildPort),
 		}, nil
 	}
 	ms.blockVSDelete = func(ctx context.Context, server string, name string) error { return nil }