diff --git a/seaweed-volume/src/storage/volume.rs b/seaweed-volume/src/storage/volume.rs
index 9a8a5a6a9..f19a7efec 100644
--- a/seaweed-volume/src/storage/volume.rs
+++ b/seaweed-volume/src/storage/volume.rs
@@ -2713,6 +2713,11 @@ impl Volume {
         needle_blob: &[u8],
         size: Size,
     ) -> Result<(), VolumeError> {
+        // nm.put on a read-only volume fails only after the blob is appended to .dat.
+        if self.is_read_only() {
+            return Err(VolumeError::ReadOnly);
+        }
+
         // Dedup check: if the same needle already exists with matching content, skip the write.
         // Matches Go's WriteNeedleBlob which reads existing needle and compares cookie+checksum+data.
         if let Some(nm) = &self.nm {
diff --git a/weed/storage/needle_map_sorted_file.go b/weed/storage/needle_map_sorted_file.go
index cbca5b3ec..8945dd46a 100644
--- a/weed/storage/needle_map_sorted_file.go
+++ b/weed/storage/needle_map_sorted_file.go
@@ -78,7 +78,7 @@ func (m *SortedFileNeedleMap) Get(key NeedleId) (element *needle_map.NeedleValue
 }
 
 func (m *SortedFileNeedleMap) Put(key NeedleId, offset Offset, size Size) error {
-	return os.ErrInvalid
+	return fmt.Errorf("needle map %s.sdx is read only: %w", m.baseFileName, os.ErrInvalid)
 }
 
 func (m *SortedFileNeedleMap) Delete(key NeedleId, offset Offset) error {
diff --git a/weed/storage/volume_write.go b/weed/storage/volume_write.go
index 9e139c757..3a8ae5f92 100644
--- a/weed/storage/volume_write.go
+++ b/weed/storage/volume_write.go
@@ -228,7 +228,8 @@ func (v *Volume) doWriteRequest(n *needle.Needle, checkCookie bool) (offset uint
 	// add to needle map
 	if !ok || uint64(nv.Offset.ToActualOffset()) < offset {
 		if err = v.nm.Put(n.Id, ToOffset(int64(offset)), n.Size); err != nil {
-			glog.V(4).Infof("failed to save in needle map %d: %v", n.Id, err)
+			err = fmt.Errorf("index needle %d of volume %d at offset %d: %w", n.Id, v.Id, offset, err)
+			glog.V(0).Info(err)
 		}
 	}
 	if v.lastModifiedTsSeconds < n.LastModified {
@@ -372,6 +373,11 @@ func (v *Volume) WriteNeedleBlob(needleId NeedleId, needleBlob []byte, size Size
 	v.dataFileAccessLock.Lock()
 	defer v.dataFileAccessLock.Unlock()
 
+	// nm.Put on a read-only volume fails only after the blob is appended to .dat.
+	if v.IsReadOnly() {
+		return fmt.Errorf("volume %d is read only", v.Id)
+	}
+
 	if MaxPossibleVolumeSize < v.nm.ContentSize()+uint64(len(needleBlob)) {
 		return fmt.Errorf("volume size limit %d exceeded! current size is %d", MaxPossibleVolumeSize, v.nm.ContentSize())
 	}
@@ -400,7 +406,8 @@ func (v *Volume) WriteNeedleBlob(needleId NeedleId, needleBlob []byte, size Size
 
 	// add to needle map
 	if err = v.nm.Put(needleId, ToOffset(int64(offset)), size); err != nil {
-		glog.V(4).Infof("failed to put in needle map %d: %v", needleId, err)
+		err = fmt.Errorf("index needle %d of volume %d at offset %d: %w", needleId, v.Id, offset, err)
+		glog.V(0).Info(err)
 	}
 
 	return err
diff --git a/weed/storage/volume_write_test.go b/weed/storage/volume_write_test.go
index f7c86f92a..dc5f5fdb5 100644
--- a/weed/storage/volume_write_test.go
+++ b/weed/storage/volume_write_test.go
@@ -167,3 +167,47 @@ func TestDestroyNonemptyVolumeWithoutOnlyEmpty(t *testing.T) {
 	}
 	assertFileExist(t, false, path)
 }
+
+// Pre-fix: the blob was appended to .dat, then rejected by SortedFileNeedleMap.Put.
+func TestWriteNeedleBlobRejectedOnReadOnlyVolume(t *testing.T) {
+	dir := t.TempDir()
+
+	v, err := NewVolume(dir, dir, "", 7, NeedleMapInMemory, &super_block.ReplicaPlacement{}, &needle.TTL{}, 0, needle.GetCurrentVersion(), 0, 0)
+	if err != nil {
+		t.Fatalf("volume creation: %v", err)
+	}
+	offset, size, _, err := v.writeNeedle2(newRandomNeedle(1), true, false)
+	if err != nil {
+		t.Fatalf("write needle: %v", err)
+	}
+	blob, err := v.ReadNeedleBlob(int64(offset), size)
+	if err != nil {
+		t.Fatalf("read needle blob: %v", err)
+	}
+	v.PersistReadOnly(true)
+	v.Close()
+
+	v, err = NewVolume(dir, dir, "", 7, NeedleMapInMemory, &super_block.ReplicaPlacement{}, &needle.TTL{}, 0, needle.GetCurrentVersion(), 0, 0)
+	if err != nil {
+		t.Fatalf("volume reload: %v", err)
+	}
+	defer v.Close()
+	if _, ok := v.nm.(*SortedFileNeedleMap); !ok {
+		t.Fatalf("reloaded read-only volume should use SortedFileNeedleMap, got %T", v.nm)
+	}
+
+	datSizeBefore, _, _ := v.DataBackend.GetStat()
+
+	err = v.WriteNeedleBlob(types.Uint64ToNeedleId(2), blob, size)
+	if err == nil {
+		t.Fatalf("expected WriteNeedleBlob to be rejected on a read-only volume")
+	}
+	if errors.Is(err, os.ErrInvalid) {
+		t.Errorf("WriteNeedleBlob should fail with a read-only error, not the needle map's os.ErrInvalid: %v", err)
+	}
+
+	datSizeAfter, _, _ := v.DataBackend.GetStat()
+	if datSizeAfter != datSizeBefore {
+		t.Errorf("read-only volume .dat grew from %d to %d, leaving an unindexed needle", datSizeBefore, datSizeAfter)
+	}
+}