diff --git a/hbs2-core/lib/HBS2/Actors/ChunkWriter.hs b/hbs2-core/lib/HBS2/Actors/ChunkWriter.hs
index bbaac0cc..55042e43 100644
--- a/hbs2-core/lib/HBS2/Actors/ChunkWriter.hs
+++ b/hbs2-core/lib/HBS2/Actors/ChunkWriter.hs
@@ -1,6 +1,6 @@
+{-# Language UndecidableInstances #-}
 module HBS2.Actors.ChunkWriter
   ( ChunkWriter
-  , ChunkId
   , newChunkWriterIO
   , runChunkWriter
   , stopChunkWriter
@@ -17,6 +17,7 @@ import HBS2.Hash
 import HBS2.Storage
 import HBS2.Defaults
 import HBS2.Clock
+import HBS2.Net.Proto.Sessions
 
 import Control.Monad.Trans.Maybe
 import Data.List qualified as L
@@ -53,6 +54,7 @@ import Control.Concurrent.STM.TBQueue qualified as Q
 import Control.Concurrent.STM.TSem qualified as Sem
 import Control.Concurrent.STM.TSem (TSem)
 
+import Data.Typeable
 import Control.Concurrent.MVar as MVar
 
 import Control.Concurrent.STM.TQueue qualified as Q0
@@ -61,13 +63,62 @@ import Control.Concurrent
 import Data.HashMap.Strict (HashMap)
 import Data.HashMap.Strict qualified as HashMap
 
---
---
---TODO: cache file handles
 
-newtype ChunkId = ChunkId FilePath
-                  deriving newtype (IsString)
-                  deriving stock (Eq,Ord,Show)
+class ( Eq salt
+      , Eq (Hash h)
+      , Hashable salt
+      , Hashable (Hash h)
+      , Typeable salt
+      , Typeable (Hash h)
+      , Hashed h ByteString
+      ) => ChunkKey salt h
+
+instance ( Hashable salt
+         , Typeable salt
+         , Eq salt
+         , Eq (Hash h)
+         , Hashable (Hash h)
+         , Typeable (Hash h)
+         , Hashed h ByteString
+         ) => ChunkKey salt h
+
+
+data Chunk h = P [(Offset, ByteString)]
+             | S (Hash h) ByteString
+
+
+instance Hashed h ByteString => Monoid (Chunk h) where
+  mempty = P []
+
+instance Hashed h ByteString => Semigroup (Chunk h) where
+  (<>) (P a) (P b) = P ( a <> b )
+
+  (<>) (S _ s1) (S _ s2) = S h3 s3
+    where
+      s3 = s1 <> s2
+      h3 = hashObject s3
+
+  (<>) p@(P{}) (S _ s) = S h3 s3
+    where
+      (S _ s1)  = toS p
+      s3 = s1 <> s
+      h3 = hashObject s3
+
+  (<>) (S _ s) p@(P{}) = S h3 s3
+    where
+      (S _ s1)  = toS p
+      s3 = s <> s1
+      h3 = hashObject s3
+
+mkP :: Offset -> ByteString -> Chunk h
+mkP o b = P [(o,b)]
+
+toS :: Hashed h ByteString => Chunk h -> Chunk h
+toS s@(S{}) = s
+toS (P xs) = S h s
+  where
+    s = foldMap snd $ L.sortBy (compare `on` fst) xs
+    h = hashObject s
 
 data ChunkWriter h m = forall a . ( MonadIO m
                                   , Storage a h ByteString m
@@ -78,8 +129,7 @@ data ChunkWriter h m = forall a . ( MonadIO m
   , pipeline     :: Pipeline IO ()
   , dir          :: FilePath
   , storage      :: a
-  , perBlock     :: !(TVar (HashMap FilePath [Handle -> IO ()]))
-  , perBlockLock :: !(TVar (HashMap FilePath TSem))
+  , perBlock     :: !(TVar (HashMap SKey (Chunk h)))
   }
 
 
@@ -130,7 +180,6 @@ newChunkWriterIO s tmp = do
   let d  = fromMaybe def tmp
 
   mt <- liftIO $ newTVarIO mempty
-  mts <- liftIO $ newTVarIO mempty
 
   running <- liftIO $ newTVarIO False
 
@@ -141,42 +190,19 @@ newChunkWriterIO s tmp = do
     , dir = d
     , storage  = s
     , perBlock = mt
-    , perBlockLock = mts
     }
 
-makeFileName :: (Hashable salt, Pretty (Hash h)) => ChunkWriter h m -> salt -> Hash h -> FilePath
-makeFileName w salt h = dir w </> suff
-  where
-    suff = show $ pretty (fromIntegral (hash salt) :: Word32) <> "@" <> pretty h
 
-delBlock :: (Hashable salt, MonadIO m, Pretty (Hash h))
-         => ChunkWriter h IO -> salt -> Hash h -> m ()
-
-delBlock w salt h = liftIO do
+delBlock :: (MonadIO m, Pretty (Hash h))
+         => ChunkWriter h IO -> SKey -> m ()
 
+delBlock w  k = liftIO do
   let cache = perBlock w
-  let se   = perBlockLock w
+  liftIO $ atomically $ TV.modifyTVar' cache $ HashMap.delete k
 
-  -- lock <- getLock w fn
-
-  flush w fn
-
-  -- atomically $ Sem.waitTSem lock
-
-  void $ runExceptT $ liftIO $ removeFile fn
-
-  liftIO $ atomically $ TV.modifyTVar' cache $ HashMap.delete fn
-  liftIO $ atomically $ TV.modifyTVar' se $ HashMap.delete fn
-
-  -- atomically $ Sem.signalTSem lock
-
-  where
-    fn = makeFileName w salt h
-
-writeChunk :: ( Hashable salt
+writeChunk :: ( ChunkKey salt h
               , MonadIO m
               , Pretty (Hash h)
-              , Hashable (Hash h), Eq (Hash h)
               )
            => ChunkWriter h m
            -> salt
@@ -188,8 +214,7 @@ writeChunk = writeChunk2
 
 
 getHash :: forall salt h m .
-           ( Hashable salt
-           , Hashed h ByteString
+           ( ChunkKey salt h
            , m ~ IO
            , Block ByteString ~ ByteString
            , Pretty (Hash h)
@@ -204,12 +229,11 @@ getHash = getHash2
 
 
 commitBlock :: forall salt h m .
-               ( Hashable salt
+               ( ChunkKey salt h
                , Hashed h ByteString
                , Block ByteString ~ ByteString
                , m ~ IO
                , Pretty (Hash h)
-               , Hashable (Hash h), Eq (Hash h)
                )
             => ChunkWriter h m
             -> salt
@@ -218,7 +242,7 @@ commitBlock :: forall salt h m .
 
 commitBlock = commitBlock2
 
-writeChunk2 :: (Hashable salt, MonadIO m, Pretty (Hash h), Hashable (Hash h), Eq (Hash h))
+writeChunk2 :: (ChunkKey salt h, MonadIO m, Pretty (Hash h))
             => ChunkWriter h m
             -> salt
             -> Hash h
@@ -228,60 +252,17 @@ writeChunk2 :: (Hashable salt, MonadIO m, Pretty (Hash h), Hashable (Hash h), Eq
 writeChunk2  w salt h o !bs = do
 
   let cache = perBlock w
-
-  let action fh = do
-        void $ runExceptT $ liftIO $ do
-          hSeek fh AbsoluteSeek (fromIntegral o)
-          B.hPutStr fh bs -- (BS.copy (B.toStrict bs))
-          hFlush fh
-
+  let k = newSKey (salt, h)
   liftIO $ do
-    atomically $ modifyTVar cache (HashMap.insertWith (<>) fn [action])
+    atomically $ modifyTVar cache (HashMap.insertWith (<>) k (mkP o bs) )
 
-  where
-    fn = makeFileName w salt h
-
-getLock w fn = do
-  _lock <- atomically $ Sem.newTSem 1
-  let locks = perBlockLock w
-  atomically $ stateTVar locks $ \x ->
-    case HashMap.lookup fn x of
-      Nothing -> (_lock, HashMap.insert fn _lock x)
-      Just s  -> (s, x)
-
-flush :: ChunkWriter h IO -> FilePath -> IO ()
-flush w fn = do
+flush :: Hashed h ByteString => ChunkWriter h IO -> SKey -> IO ()
+flush w k = do
   let cache = perBlock w
+  void $ atomically $ modifyTVar cache (HashMap.adjust toS k)
 
-  let pip = pipeline w
-
-
-  q <- liftIO $ Q.newTBQueueIO 1
-
-  -- addJob pip $ do
-
-  lock <- getLock w fn
-
-  race (pause (2 :: Timeout 'Seconds)) $ do
-    void $ runExceptT $ liftIO $ do
-      atomically $ Sem.waitTSem lock
-      mbactions <- atomically $ stateTVar cache (\v -> (HashMap.lookup fn v, HashMap.delete fn v))
-      maybe1 mbactions (pure ()) $ \actions -> do
-        withBinaryFile fn ReadWriteMode $ \h -> do
-            for_ actions $ \f -> f h
-
-  atomically $ Sem.signalTSem lock
-  void $ liftIO $ atomically $ Q.writeTBQueue q ()
-
-  void $ liftIO $ atomically $ Q.readTBQueue q
-
-
--- Blocking!
--- we need to write last chunk before this will happen
--- FIXME: incremental calculation,
---        streaming, blah-blah
 getHash2 :: forall salt h m .
-           ( Hashable salt
+           ( ChunkKey salt h
            , Hashed h ByteString
            , m ~ IO
            , Block ByteString ~ ByteString
@@ -294,26 +275,19 @@ getHash2 :: forall salt h m .
          -> m (Maybe (Hash h))
 
 getHash2 w salt h = do
-
-  flush w fn
-
-  runMaybeT $ do
-    res <- liftIO $! runExceptT $ liftIO do
-                     ( B.readFile fn  >>= \s -> pure $ hashObject @h s )
-
-    MaybeT $! pure $! either (const Nothing) Just res
-
-  where
-    fn = makeFileName w salt h
+  let k = newSKey (salt, h)
+  chunk <- readTVarIO (perBlock w) <&> fmap toS . HashMap.lookup k
+  case chunk of
+    Just (S h1 _) -> pure (Just h1)
+    _             -> pure Nothing
 
 
 commitBlock2 :: forall salt h m .
-               ( Hashable salt
+               ( ChunkKey salt h
                , Hashed h ByteString
                , Block ByteString ~ ByteString
                , m ~ IO
                , Pretty (Hash h)
-               , Hashable (Hash h), Eq (Hash h)
                )
             => ChunkWriter h m
             -> salt
@@ -321,22 +295,11 @@ commitBlock2 :: forall salt h m .
             -> m ()
 
 commitBlock2 w@(ChunkWriter {storage = stor}) salt h = do
+  let k = newSKey (salt, h)
+  chunk <- readTVarIO (perBlock w) <&> fmap toS . HashMap.lookup k
 
-  flush w fn
-
-  exists <- doesFileExist fn
-
-  when exists $ do
-
-    res <- liftIO $ runExceptT $! liftIO ( B.readFile fn )
-
-    case res of
-      Left _ -> pure ()
-      Right s -> do
-        void $ putBlock stor s
-        delBlock w salt h
-
-  where
-    fn = makeFileName w salt h
+  case chunk of
+    Just (S _ s) -> void $ putBlock stor s >> delBlock w k
+    _            -> pure () -- FIXME: error
 
 
diff --git a/hbs2-core/lib/HBS2/Net/Proto/Sessions.hs b/hbs2-core/lib/HBS2/Net/Proto/Sessions.hs
index d40faa7f..5d35f6b1 100644
--- a/hbs2-core/lib/HBS2/Net/Proto/Sessions.hs
+++ b/hbs2-core/lib/HBS2/Net/Proto/Sessions.hs
@@ -1,4 +1,3 @@
-{-# Language FunctionalDependencies #-}
 module HBS2.Net.Proto.Sessions where
 
 import HBS2.Net.Proto.Types
@@ -9,27 +8,26 @@ import Data.Hashable
 import Type.Reflection
 import Data.Kind
 
-data SKey = forall a . (Unkey a, Eq a, Hashable a) => SKey (Proxy a) SomeTypeRep Dynamic
+data SKey = forall a . (Unkey a, Eq a, Hashable a) => SKey !(Proxy a) !SomeTypeRep !Dynamic
 
 class Typeable a => Unkey a where
   unKey :: Proxy a -> Dynamic -> Maybe a
 
 instance Typeable a => Unkey a where
   unKey _ = fromDynamic @a
+  {-# INLINE unKey #-}
 
 newSKey :: forall a . (Eq a, Typeable a, Unkey a, Hashable a) => a -> SKey
 newSKey s = SKey (Proxy @a) (someTypeRep (Proxy @a)) (toDyn s)
+{-# INLINE newSKey #-}
 
 
 instance Hashable SKey where
-  hashWithSalt s (SKey p t d) = hashWithSalt s (p, t, unKey p d)
+  hashWithSalt s (SKey p t d) = hashWithSalt s (t, unKey p d)
 
 
 instance Eq SKey where
-  (==) (SKey p1 ty1 a) (SKey p2 ty2 b) =
-       ty1 == ty2
-    && unKey p1 a == unKey p1 b
-    && unKey p2 a == unKey p2 b
+  (==) (SKey p1 ty1 a) (SKey p2 ty2 b) = ty1 == ty2 && unKey p1 a == unKey p1 b
 
 
 data family SessionKey  e p :: Type
diff --git a/hbs2-tests/test/TestChunkWriter.hs b/hbs2-tests/test/TestChunkWriter.hs
index b5f8f4fa..c1fe9220 100644
--- a/hbs2-tests/test/TestChunkWriter.hs
+++ b/hbs2-tests/test/TestChunkWriter.hs
@@ -52,7 +52,7 @@ main = do
 
     w2 <- replicateM 8 $ async $ runChunkWriter cw
 
-    let times = 500
+    let times = 1000
 
     let info = show $ "writing" <+> pretty (show (realToFrac size / (1024*1024) :: Fixed E2))
                                 <+> "mb"
@@ -67,9 +67,10 @@ main = do
 
           let psz = calcChunks (fromIntegral size) (fromIntegral chu)
 
-          psz' <- shuffleM psz
+          psz' <- pure psz
+          -- psz' <- shuffleM psz
 
-          forConcurrently_ psz' $ \(o,s) -> do
+          forM_ psz' $ \(o,s) -> do
             let t = B8.take s $ B8.drop o bytes
             writeChunk cw 1 hash (fromIntegral o) t