diff --git a/apps/emqx_ft/src/emqx_ft_assembler_sup.erl b/apps/emqx_ft/src/emqx_ft_assembler_sup.erl
index e837d96f1..b60949a5e 100644
--- a/apps/emqx_ft/src/emqx_ft_assembler_sup.erl
+++ b/apps/emqx_ft/src/emqx_ft_assembler_sup.erl
@@ -36,7 +36,7 @@ start_child(Storage, Transfer, Callback) ->
 init(_) ->
     SupFlags = #{
         strategy => one_for_one,
-        intensity => 100,
+        intensity => 10,
         period => 1000
     },
     {ok, {SupFlags, []}}.
diff --git a/apps/emqx_ft/src/emqx_ft_storage_fs.erl b/apps/emqx_ft/src/emqx_ft_storage_fs.erl
index 15efa142b..cce7cc19e 100644
--- a/apps/emqx_ft/src/emqx_ft_storage_fs.erl
+++ b/apps/emqx_ft/src/emqx_ft_storage_fs.erl
@@ -24,6 +24,7 @@
 -export([store_filemeta/3]).
 -export([store_segment/3]).
 -export([list/2]).
+-export([read_segment/5]).
 -export([assemble/3]).
 
 -export([open_file/3]).
@@ -154,6 +155,28 @@ list(Storage, Transfer) ->
             Error
     end.
 
+-spec read_segment(
+    storage(), transfer(), filefrag(segmentinfo()), offset(), _Size :: non_neg_integer()
+) ->
+    {ok, _Content :: iodata()} | {error, _TODO}.
+read_segment(_Storage, _Transfer, Segment, Offset, Size) ->
+    Filepath = maps:get(path, Segment),
+    case file:open(Filepath, [raw, read]) of
+        {ok, IoDevice} ->
+            Read = file:pread(IoDevice, Offset, Size),
+            ok = file:close(IoDevice),
+            case Read of
+                {ok, Content} ->
+                    {ok, Content};
+                eof ->
+                    {error, eof};
+                {error, Reason} ->
+                    {error, Reason}
+            end;
+        {error, Reason} ->
+            {error, Reason}
+    end.
+
 -spec assemble(storage(), transfer(), fun((ok | {error, term()}) -> any())) ->
     % {ok, _Assembler :: pid()} | {error, incomplete} | {error, badrpc} | {error, _TODO}.
     {ok, _Assembler :: pid()} | {error, _TODO}.
@@ -359,18 +382,18 @@ safe_decode(Content, DecodeFun) ->
     end.
 
 write_file_atomic(Filepath, Content) when is_binary(Content) ->
+    TempFilepath = mk_temp_filepath(Filepath),
     Result = emqx_misc:pipeline(
         [
             fun filelib:ensure_dir/1,
-            fun mk_temp_filepath/1,
             fun write_contents/2,
-            fun mv_temp_file/1
+            fun(FP) -> mv_temp_file(Filepath, FP) end
         ],
-        Filepath,
+        TempFilepath,
         Content
     ),
     case Result of
-        {ok, {Filepath, TempFilepath}, _} ->
+        {ok, _, _} ->
             _ = file:delete(TempFilepath),
             ok;
         {error, Reason, _} ->
@@ -381,13 +404,20 @@ mk_temp_filepath(Filepath) ->
     Dirname = filename:dirname(Filepath),
     Filename = filename:basename(Filepath),
     Unique = erlang:unique_integer([positive]),
-    TempFilepath = filename:join(Dirname, ?TEMP ++ integer_to_list(Unique) ++ "." ++ Filename),
-    {Filepath, TempFilepath}.
+    filename:join(Dirname, mk_filename([?TEMP, Unique, ".", Filename])).
 
-write_contents({_Filepath, TempFilepath}, Content) ->
-    file:write_file(TempFilepath, Content).
+mk_filename(Comps) ->
+    lists:append(lists:map(fun mk_filename_component/1, Comps)).
 
-mv_temp_file({Filepath, TempFilepath}) ->
+mk_filename_component(I) when is_integer(I) -> integer_to_list(I);
+mk_filename_component(A) when is_atom(A) -> atom_to_list(A);
+mk_filename_component(B) when is_binary(B) -> unicode:characters_to_list(B);
+mk_filename_component(S) when is_list(S) -> S.
+
+write_contents(Filepath, Content) ->
+    file:write_file(Filepath, Content).
+
+mv_temp_file(Filepath, TempFilepath) ->
     file:rename(TempFilepath, Filepath).
 
 touch_file(Filepath) ->
@@ -398,21 +428,22 @@ filtermap_files(Fun, Dirname, Filenames) ->
     lists:filtermap(fun(Filename) -> Fun(Dirname, Filename) end, Filenames).
 
 mk_filefrag(Dirname, Filename = ?MANIFEST) ->
-    mk_filefrag(Dirname, Filename, fun read_filemeta/2);
+    mk_filefrag(Dirname, Filename, filemeta, fun read_filemeta/2);
 mk_filefrag(Dirname, Filename = ?SEGMENT ++ _) ->
-    mk_filefrag(Dirname, Filename, fun read_segmentinfo/2);
+    mk_filefrag(Dirname, Filename, segment, fun read_segmentinfo/2);
 mk_filefrag(_Dirname, _) ->
     false.
 
-mk_filefrag(Dirname, Filename, Fun) ->
+mk_filefrag(Dirname, Filename, Tag, Fun) ->
     Filepath = filename:join(Dirname, Filename),
-    Fileinfo = file:read_file_info(Filepath),
+    % TODO error handling?
+    {ok, Fileinfo} = file:read_file_info(Filepath),
     case Fun(Filename, Filepath) of
         {ok, Frag} ->
             {true, #{
                 path => Filepath,
                 timestamp => Fileinfo#file_info.mtime,
-                fragment => Frag
+                fragment => {Tag, Frag}
             }};
         {error, _Reason} ->
             false