diff --git a/other/java/client/src/main/proto/filer.proto b/other/java/client/src/main/proto/filer.proto
index d7067def0..2269c563c 100644
--- a/other/java/client/src/main/proto/filer.proto
+++ b/other/java/client/src/main/proto/filer.proto
@@ -294,6 +294,7 @@ message AssignVolumeRequest {
     string rack = 7;
     string data_node = 9;
     string disk_type = 8;
+    uint64 expected_data_size = 10; // hint for size-aware volume selection
 }
 
 message AssignVolumeResponse {
diff --git a/seaweed-volume/proto/master.proto b/seaweed-volume/proto/master.proto
index 8289cd233..f3253c2a4 100644
--- a/seaweed-volume/proto/master.proto
+++ b/seaweed-volume/proto/master.proto
@@ -231,6 +231,7 @@ message AssignRequest {
   uint32 memory_map_max_size_mb = 8;
   uint32 writable_volume_count = 9;
   string disk_type = 10;
+  uint64 expected_data_size = 11; // hint for size-aware volume selection
 }
 
 message VolumeGrowRequest {
diff --git a/weed/operation/assign_file_id.go b/weed/operation/assign_file_id.go
index 5609bf8ac..525ce515d 100644
--- a/weed/operation/assign_file_id.go
+++ b/weed/operation/assign_file_id.go
@@ -26,6 +26,7 @@ type VolumeAssignRequest struct {
 	Rack                string
 	DataNode            string
 	WritableVolumeCount uint32
+	ExpectedDataSize    uint64
 }
 
 type AssignResult struct {
@@ -86,6 +87,7 @@ func Assign(ctx context.Context, masterFn GetMasterFn, grpcDialOption grpc.DialO
 						Rack:                request.Rack,
 						DataNode:            request.DataNode,
 						WritableVolumeCount: request.WritableVolumeCount,
+						ExpectedDataSize:    request.ExpectedDataSize,
 					}
 					resp, grpcErr := masterClient.Assign(attemptCtx, req)
 					if grpcErr != nil {
diff --git a/weed/pb/filer.proto b/weed/pb/filer.proto
index b06d7ffa9..7dd8c6ab2 100644
--- a/weed/pb/filer.proto
+++ b/weed/pb/filer.proto
@@ -297,6 +297,7 @@ message AssignVolumeRequest {
     string rack = 7;
     string data_node = 9;
     string disk_type = 8;
+    uint64 expected_data_size = 10; // hint for size-aware volume selection
 }
 
 message AssignVolumeResponse {
diff --git a/weed/pb/filer_pb/filer.pb.go b/weed/pb/filer_pb/filer.pb.go
index 44ccacfa4..e82c1b865 100644
--- a/weed/pb/filer_pb/filer.pb.go
+++ b/weed/pb/filer_pb/filer.pb.go
@@ -1879,18 +1879,19 @@ func (x *StreamRenameEntryResponse) GetTsNs() int64 {
 }
 
 type AssignVolumeRequest struct {
-	state         protoimpl.MessageState `protogen:"open.v1"`
-	Count         int32                  `protobuf:"varint,1,opt,name=count,proto3" json:"count,omitempty"`
-	Collection    string                 `protobuf:"bytes,2,opt,name=collection,proto3" json:"collection,omitempty"`
-	Replication   string                 `protobuf:"bytes,3,opt,name=replication,proto3" json:"replication,omitempty"`
-	TtlSec        int32                  `protobuf:"varint,4,opt,name=ttl_sec,json=ttlSec,proto3" json:"ttl_sec,omitempty"`
-	DataCenter    string                 `protobuf:"bytes,5,opt,name=data_center,json=dataCenter,proto3" json:"data_center,omitempty"`
-	Path          string                 `protobuf:"bytes,6,opt,name=path,proto3" json:"path,omitempty"`
-	Rack          string                 `protobuf:"bytes,7,opt,name=rack,proto3" json:"rack,omitempty"`
-	DataNode      string                 `protobuf:"bytes,9,opt,name=data_node,json=dataNode,proto3" json:"data_node,omitempty"`
-	DiskType      string                 `protobuf:"bytes,8,opt,name=disk_type,json=diskType,proto3" json:"disk_type,omitempty"`
-	unknownFields protoimpl.UnknownFields
-	sizeCache     protoimpl.SizeCache
+	state            protoimpl.MessageState `protogen:"open.v1"`
+	Count            int32                  `protobuf:"varint,1,opt,name=count,proto3" json:"count,omitempty"`
+	Collection       string                 `protobuf:"bytes,2,opt,name=collection,proto3" json:"collection,omitempty"`
+	Replication      string                 `protobuf:"bytes,3,opt,name=replication,proto3" json:"replication,omitempty"`
+	TtlSec           int32                  `protobuf:"varint,4,opt,name=ttl_sec,json=ttlSec,proto3" json:"ttl_sec,omitempty"`
+	DataCenter       string                 `protobuf:"bytes,5,opt,name=data_center,json=dataCenter,proto3" json:"data_center,omitempty"`
+	Path             string                 `protobuf:"bytes,6,opt,name=path,proto3" json:"path,omitempty"`
+	Rack             string                 `protobuf:"bytes,7,opt,name=rack,proto3" json:"rack,omitempty"`
+	DataNode         string                 `protobuf:"bytes,9,opt,name=data_node,json=dataNode,proto3" json:"data_node,omitempty"`
+	DiskType         string                 `protobuf:"bytes,8,opt,name=disk_type,json=diskType,proto3" json:"disk_type,omitempty"`
+	ExpectedDataSize uint64                 `protobuf:"varint,10,opt,name=expected_data_size,json=expectedDataSize,proto3" json:"expected_data_size,omitempty"` // hint for size-aware volume selection
+	unknownFields    protoimpl.UnknownFields
+	sizeCache        protoimpl.SizeCache
 }
 
 func (x *AssignVolumeRequest) Reset() {
@@ -1986,6 +1987,13 @@ func (x *AssignVolumeRequest) GetDiskType() string {
 	return ""
 }
 
+func (x *AssignVolumeRequest) GetExpectedDataSize() uint64 {
+	if x != nil {
+		return x.ExpectedDataSize
+	}
+	return 0
+}
+
 type AssignVolumeResponse struct {
 	state         protoimpl.MessageState `protogen:"open.v1"`
 	FileId        string                 `protobuf:"bytes,1,opt,name=file_id,json=fileId,proto3" json:"file_id,omitempty"`
@@ -5248,7 +5256,7 @@ const file_filer_proto_rawDesc = "" +
 	"\x19StreamRenameEntryResponse\x12\x1c\n" +
 	"\tdirectory\x18\x01 \x01(\tR\tdirectory\x12J\n" +
 	"\x12event_notification\x18\x02 \x01(\v2\x1b.filer_pb.EventNotificationR\x11eventNotification\x12\x13\n" +
-	"\x05ts_ns\x18\x03 \x01(\x03R\x04tsNs\"\x89\x02\n" +
+	"\x05ts_ns\x18\x03 \x01(\x03R\x04tsNs\"\xb7\x02\n" +
 	"\x13AssignVolumeRequest\x12\x14\n" +
 	"\x05count\x18\x01 \x01(\x05R\x05count\x12\x1e\n" +
 	"\n" +
@@ -5261,7 +5269,9 @@ const file_filer_proto_rawDesc = "" +
 	"\x04path\x18\x06 \x01(\tR\x04path\x12\x12\n" +
 	"\x04rack\x18\a \x01(\tR\x04rack\x12\x1b\n" +
 	"\tdata_node\x18\t \x01(\tR\bdataNode\x12\x1b\n" +
-	"\tdisk_type\x18\b \x01(\tR\bdiskType\"\xe1\x01\n" +
+	"\tdisk_type\x18\b \x01(\tR\bdiskType\x12,\n" +
+	"\x12expected_data_size\x18\n" +
+	" \x01(\x04R\x10expectedDataSize\"\xe1\x01\n" +
 	"\x14AssignVolumeResponse\x12\x17\n" +
 	"\afile_id\x18\x01 \x01(\tR\x06fileId\x12\x14\n" +
 	"\x05count\x18\x04 \x01(\x05R\x05count\x12\x12\n" +
diff --git a/weed/pb/master.proto b/weed/pb/master.proto
index 0a60847e1..c127bafb1 100644
--- a/weed/pb/master.proto
+++ b/weed/pb/master.proto
@@ -242,6 +242,7 @@ message AssignRequest {
   uint32 memory_map_max_size_mb = 8;
   uint32 writable_volume_count = 9;
   string disk_type = 10;
+  uint64 expected_data_size = 11; // hint for size-aware volume selection
 }
 
 message VolumeGrowRequest {
diff --git a/weed/pb/master_pb/master.pb.go b/weed/pb/master_pb/master.pb.go
index 7e161d3fb..24d1ab64f 100644
--- a/weed/pb/master_pb/master.pb.go
+++ b/weed/pb/master_pb/master.pb.go
@@ -1430,6 +1430,7 @@ type AssignRequest struct {
 	MemoryMapMaxSizeMb  uint32                 `protobuf:"varint,8,opt,name=memory_map_max_size_mb,json=memoryMapMaxSizeMb,proto3" json:"memory_map_max_size_mb,omitempty"`
 	WritableVolumeCount uint32                 `protobuf:"varint,9,opt,name=writable_volume_count,json=writableVolumeCount,proto3" json:"writable_volume_count,omitempty"`
 	DiskType            string                 `protobuf:"bytes,10,opt,name=disk_type,json=diskType,proto3" json:"disk_type,omitempty"`
+	ExpectedDataSize    uint64                 `protobuf:"varint,11,opt,name=expected_data_size,json=expectedDataSize,proto3" json:"expected_data_size,omitempty"` // hint for size-aware volume selection
 	unknownFields       protoimpl.UnknownFields
 	sizeCache           protoimpl.SizeCache
 }
@@ -1534,6 +1535,13 @@ func (x *AssignRequest) GetDiskType() string {
 	return ""
 }
 
+func (x *AssignRequest) GetExpectedDataSize() uint64 {
+	if x != nil {
+		return x.ExpectedDataSize
+	}
+	return 0
+}
+
 type VolumeGrowRequest struct {
 	state               protoimpl.MessageState `protogen:"open.v1"`
 	WritableVolumeCount uint32                 `protobuf:"varint,1,opt,name=writable_volume_count,json=writableVolumeCount,proto3" json:"writable_volume_count,omitempty"`
@@ -4500,7 +4508,7 @@ const file_master_proto_rawDesc = "" +
 	"public_url\x18\x02 \x01(\tR\tpublicUrl\x12\x1b\n" +
 	"\tgrpc_port\x18\x03 \x01(\rR\bgrpcPort\x12\x1f\n" +
 	"\vdata_center\x18\x04 \x01(\tR\n" +
-	"dataCenter\"\xd0\x02\n" +
+	"dataCenter\"\xfe\x02\n" +
 	"\rAssignRequest\x12\x14\n" +
 	"\x05count\x18\x01 \x01(\x04R\x05count\x12 \n" +
 	"\vreplication\x18\x02 \x01(\tR\vreplication\x12\x1e\n" +
@@ -4515,7 +4523,8 @@ const file_master_proto_rawDesc = "" +
 	"\x16memory_map_max_size_mb\x18\b \x01(\rR\x12memoryMapMaxSizeMb\x122\n" +
 	"\x15writable_volume_count\x18\t \x01(\rR\x13writableVolumeCount\x12\x1b\n" +
 	"\tdisk_type\x18\n" +
-	" \x01(\tR\bdiskType\"\xbe\x02\n" +
+	" \x01(\tR\bdiskType\x12,\n" +
+	"\x12expected_data_size\x18\v \x01(\x04R\x10expectedDataSize\"\xbe\x02\n" +
 	"\x11VolumeGrowRequest\x122\n" +
 	"\x15writable_volume_count\x18\x01 \x01(\rR\x13writableVolumeCount\x12 \n" +
 	"\vreplication\x18\x02 \x01(\tR\vreplication\x12\x1e\n" +
diff --git a/weed/server/common.go b/weed/server/common.go
index 9a6b2a7da..2d3c55466 100644
--- a/weed/server/common.go
+++ b/weed/server/common.go
@@ -154,13 +154,14 @@ func submitForClientHandler(w http.ResponseWriter, r *http.Request, masterFn ope
 		}
 	}
 	ar := &operation.VolumeAssignRequest{
-		Count:       count,
-		DataCenter:  r.FormValue("dataCenter"),
-		Rack:        r.FormValue("rack"),
-		Replication: r.FormValue("replication"),
-		Collection:  r.FormValue("collection"),
-		Ttl:         r.FormValue("ttl"),
-		DiskType:    r.FormValue("disk"),
+		Count:            count,
+		DataCenter:       r.FormValue("dataCenter"),
+		Rack:             r.FormValue("rack"),
+		Replication:      r.FormValue("replication"),
+		Collection:       r.FormValue("collection"),
+		Ttl:              r.FormValue("ttl"),
+		DiskType:         r.FormValue("disk"),
+		ExpectedDataSize: uint64(max(int64(0), int64(pu.OriginalDataSize))),
 	}
 	assignResult, ae := operation.Assign(ctx, masterFn, grpcDialOption, ar)
 	if ae != nil {
diff --git a/weed/server/filer_grpc_server.go b/weed/server/filer_grpc_server.go
index e8f026943..76dcb4dee 100644
--- a/weed/server/filer_grpc_server.go
+++ b/weed/server/filer_grpc_server.go
@@ -395,6 +395,10 @@ func (fs *FilerServer) AssignVolume(ctx context.Context, req *filer_pb.AssignVol
 	}
 
 	assignRequest, altRequest := so.ToAssignRequests(int(req.Count))
+	assignRequest.ExpectedDataSize = req.ExpectedDataSize
+	if altRequest != nil {
+		altRequest.ExpectedDataSize = req.ExpectedDataSize
+	}
 
 	assignResult, err := operation.Assign(ctx, fs.filer.GetMaster, fs.grpcDialOption, assignRequest, altRequest)
 	if err != nil {
diff --git a/weed/server/master_grpc_server_assign.go b/weed/server/master_grpc_server_assign.go
index 4911c49a3..3a8ac6eff 100644
--- a/weed/server/master_grpc_server_assign.go
+++ b/weed/server/master_grpc_server_assign.go
@@ -111,7 +111,7 @@ func (ms *MasterServer) Assign(ctx context.Context, req *master_pb.AssignRequest
 	)
 
 	for time.Now().Sub(startTime) < maxTimeout {
-		fid, count, dnList, shouldGrow, err := ms.Topo.PickForWrite(req.Count, option, vl)
+		fid, count, dnList, shouldGrow, err := ms.Topo.PickForWrite(req.Count, option, vl, req.ExpectedDataSize)
 		if shouldGrow && !vl.HasGrowRequest() && !ms.option.VolumeGrowthDisabled {
 			if err != nil && ms.Topo.AvailableSpaceFor(option) <= 0 {
 				err = fmt.Errorf("%s and no free volumes left for %s", err.Error(), option.String())
diff --git a/weed/server/master_server_handlers.go b/weed/server/master_server_handlers.go
index 3bca8eadc..25ee1dfd5 100644
--- a/weed/server/master_server_handlers.go
+++ b/weed/server/master_server_handlers.go
@@ -144,6 +144,11 @@ func (ms *MasterServer) dirAssignHandler(w http.ResponseWriter, r *http.Request)
 		writableVolumeCount = 0
 	}
 
+	expectedDataSize, e := strconv.ParseUint(r.FormValue("dataSize"), 10, 64)
+	if e != nil {
+		expectedDataSize = 0
+	}
+
 	option, err := ms.getVolumeGrowOption(r)
 	if err != nil {
 		writeJsonQuiet(w, r, http.StatusNotAcceptable, operation.AssignResult{Error: err.Error()})
@@ -166,7 +171,7 @@ func (ms *MasterServer) dirAssignHandler(w http.ResponseWriter, r *http.Request)
 	}
 
 	for time.Since(startTime) < maxTimeout {
-		fid, count, dnList, shouldGrow, err := ms.Topo.PickForWrite(requestedCount, option, vl)
+		fid, count, dnList, shouldGrow, err := ms.Topo.PickForWrite(requestedCount, option, vl, expectedDataSize)
 		if shouldGrow && !vl.HasGrowRequest() && !ms.option.VolumeGrowthDisabled {
 			glog.V(0).Infof("dirAssign volume growth %v from %v", option.String(), r.RemoteAddr)
 			if err != nil && ms.Topo.AvailableSpaceFor(option) <= 0 {
diff --git a/weed/topology/topology.go b/weed/topology/topology.go
index ba90b8dae..0c26bfd86 100644
--- a/weed/topology/topology.go
+++ b/weed/topology/topology.go
@@ -320,12 +320,11 @@ func (t *Topology) NextVolumeId() (needle.VolumeId, error) {
 	return next, nil
 }
 
-// EstimatedNeedleSizeBytes is the assumed size per assigned file ID, used to
-// estimate pending bytes between heartbeats. Intentionally coarse — it only
-// needs to spread load, not be precise.
-const EstimatedNeedleSizeBytes = 1024 * 1024 // 1 MB
+// DefaultNeedleSizeEstimate is the fallback per-file-ID size estimate when
+// the client does not provide an expected data size.
+const DefaultNeedleSizeEstimate uint64 = 1024 * 1024 // 1 MB
 
-func (t *Topology) PickForWrite(requestedCount uint64, option *VolumeGrowOption, volumeLayout *VolumeLayout) (fileId string, count uint64, volumeLocationList *VolumeLocationList, shouldGrow bool, err error) {
+func (t *Topology) PickForWrite(requestedCount uint64, option *VolumeGrowOption, volumeLayout *VolumeLayout, expectedDataSize uint64) (fileId string, count uint64, volumeLocationList *VolumeLocationList, shouldGrow bool, err error) {
 	var vid needle.VolumeId
 	vid, count, volumeLocationList, shouldGrow, err = volumeLayout.PickForWrite(requestedCount, option)
 	if err != nil {
@@ -335,8 +334,12 @@ func (t *Topology) PickForWrite(requestedCount uint64, option *VolumeGrowOption,
 		return "", 0, nil, shouldGrow, fmt.Errorf("%s available for collection:%s replication:%s ttl:%s", NoWritableVolumes, option.Collection, option.ReplicaPlacement.String(), option.Ttl.String())
 	}
 	// Track estimated assigned bytes to spread load between heartbeats.
-	// Compute in uint64 and cap to avoid overflow on the int64 cast.
-	pendingBytes := min(uint64(count)*EstimatedNeedleSizeBytes, uint64(math.MaxInt64))
+	// Use the client hint if provided, otherwise fall back to 1MB estimate.
+	sizePerFile := DefaultNeedleSizeEstimate
+	if expectedDataSize > 0 {
+		sizePerFile = expectedDataSize
+	}
+	pendingBytes := min(uint64(count)*sizePerFile, uint64(math.MaxInt64))
 	volumeLayout.RecordAssign(vid, int64(pendingBytes))
 	nextFileId := t.Sequence.NextFileId(requestedCount)
 	fileId = needle.NewFileId(vid, nextFileId, rand.Uint32()).String()
diff --git a/weed/topology/volume_growth_test.go b/weed/topology/volume_growth_test.go
index 9bf3f3747..bc9c0c640 100644
--- a/weed/topology/volume_growth_test.go
+++ b/weed/topology/volume_growth_test.go
@@ -433,7 +433,7 @@ func TestPickForWrite(t *testing.T) {
 						continue
 					}
 					volumeGrowOption.DataNode = dn
-					fileId, count, _, shouldGrow, err := topo.PickForWrite(1, volumeGrowOption, vl)
+					fileId, count, _, shouldGrow, err := topo.PickForWrite(1, volumeGrowOption, vl, 0)
 					if dc == "dc0" {
 						if err == nil || count != 0 || !shouldGrow {
 							fmt.Println(dc, r, dn, "pick for write should be with error")
@@ -452,6 +452,18 @@ func TestPickForWrite(t *testing.T) {
 						fmt.Println(dc, r, dn, "pick for write error : not should grow")
 						t.Fail()
 					}
+
+					// Also verify with a non-zero expectedDataSize hint
+					if dc != "dc0" {
+						fileId2, count2, _, shouldGrow2, err2 := topo.PickForWrite(1, volumeGrowOption, vl, 1024)
+						if err2 != nil {
+							fmt.Println(dc, r, dn, "pick for write with size hint error:", err2)
+							t.Fail()
+						} else if count2 == 0 || len(fileId2) == 0 || shouldGrow2 {
+							fmt.Println(dc, r, dn, "pick for write with size hint unexpected result")
+							t.Fail()
+						}
+					}
 				}
 			}
 		}