fix unclaimed spaces calculation when volumePreallocate is enabled (#6063)

the calculation of `unclaimedSpaces` only needs to subtract `unusedSpace` when `preallocate` is not enabled.

Signed-off-by: LHHDZ <shichanglin5@qq.com>

weed/server/master_grpc_server.go

@@ -151,6 +151,7 @@ func (ms *MasterServer) SendHeartbeat(stream master_pb.Seaweed_SendHeartbeatServ
 
 			if err := stream.Send(&master_pb.HeartbeatResponse{
 				VolumeSizeLimit: uint64(ms.option.VolumeSizeLimitMB) * 1024 * 1024,
+				Preallocate:     ms.preallocateSize > 0,
 			}); err != nil {
 				glog.Warningf("SendHeartbeat.Send volume size to %s:%d %v", dn.Ip, dn.Port, err)
 				return err

weed/server/volume_grpc_client_to_master.go

@@ -130,8 +130,16 @@ func (vs *VolumeServer) doHeartbeat(masterAddress pb.ServerAddress, grpcDialOpti
 				glog.Errorf("Shut down Volume Server due to duplicate volume directories: %v", duplicateDir)
 				os.Exit(1)
 			}
+			volumeOptsChanged := false
+			if vs.store.GetPreallocate() != in.GetPreallocate() {
+				vs.store.SetPreallocate(in.GetPreallocate())
+				volumeOptsChanged = true
+			}
 			if in.GetVolumeSizeLimit() != 0 && vs.store.GetVolumeSizeLimit() != in.GetVolumeSizeLimit() {
 				vs.store.SetVolumeSizeLimit(in.GetVolumeSizeLimit())
+				volumeOptsChanged = true
+			}
+			if volumeOptsChanged {
 				if vs.store.MaybeAdjustVolumeMax() {
 					if err = stream.Send(vs.store.CollectHeartbeat()); err != nil {
 						glog.V(0).Infof("Volume Server Failed to talk with master %s: %v", vs.currentMaster, err)