diff --git a/src/journal/src/Journal/Internal/ByteBuffer.hs b/src/journal/src/Journal/Internal/ByteBuffer.hs
index 05b4150a..58b113f9 100644
--- a/src/journal/src/Journal/Internal/ByteBuffer.hs
+++ b/src/journal/src/Journal/Internal/ByteBuffer.hs
@@ -1,4 +1,5 @@
 {-# LANGUAGE MagicHash #-}
+{-# LANGUAGE GeneralizedNewtypeDeriving #-}
 {-# LANGUAGE UnboxedTuples #-}
 
 module Journal.Internal.ByteBuffer where
@@ -8,68 +9,98 @@ import Data.IORef
 import Foreign
 import GHC.ForeignPtr
 import GHC.Exts
+import GHC.Types
+import GHC.IO
 import System.Posix.IO (openFd, defaultFileFlags, OpenMode(ReadWrite))
 
 import Journal.Internal.Mmap
 
 ------------------------------------------------------------------------
--- * Type
+-- * Types
+
+type MBArray = MutableByteArray# RealWorld
 
 data ByteBuffer = ByteBuffer
-  { bbAddr     :: {-# UNPACK #-} !Addr#
-  , bbCapacity :: {-# UNPACK #-} !Int
-  , bbLimit    :: {-# UNPACK #-} !(IORef Int)
-  , bbPosition :: {-# UNPACK #-} !(IORef Int)
-  , bbMark     :: {-# UNPACK #-} !(IORef Int)
+  { bbData     :: {-# UNPACK #-} !MBArray
+  , bbCapacity :: {-# UNPACK #-} !Capacity
+  , bbLimit    :: {-# UNPACK #-} !(IORef Limit)
+  , bbPosition :: {-# UNPACK #-} !(IORef Position)
+  , bbMark     :: {-# UNPACK #-} !(IORef Position)
+  , bbSlice    :: {-# UNPACK #-} !(IORef Slice)
   }
 
-newByteBuffer :: Addr# -> Int -> Int -> Int -> IO ByteBuffer
-newByteBuffer addr# capa lim pos =
-  ByteBuffer addr# capa <$> newIORef lim <*> newIORef pos <*> newIORef (-1)
+newtype Capacity = Capacity Int
+  deriving (Num, Integral, Real, Ord, Eq, Enum)
+
+newtype Limit = Limit Int
+  deriving (Num, Integral, Real, Ord, Eq, Enum)
+
+newtype Position = Position Int
+  deriving (Num, Integral, Real, Ord, Eq, Enum)
+
+newtype Slice = Slice Int
+  deriving (Num, Integral, Real, Ord, Eq, Enum)
+
+------------------------------------------------------------------------
+
+newByteBuffer :: MBArray -> Capacity -> Limit -> Position -> Maybe (IORef Slice)
+              -> IO ByteBuffer
+newByteBuffer mba# capa lim pos mSli
+  = ByteBuffer mba# capa
+  <$> newIORef lim
+  <*> newIORef pos
+  <*> newIORef (-1)
+  <*> maybe (newIORef 0) return mSli
 
 bbPtr :: ByteBuffer -> Ptr a
-bbPtr (ByteBuffer addr# _ _ _ _) = Ptr addr#
+bbPtr (ByteBuffer mba# _ _ _ _ _) = Ptr (byteArrayContents# (unsafeCoerce# mba#))
 {-# INLINE bbPtr #-}
 
-getCapacity :: ByteBuffer -> Int
+getCapacity :: ByteBuffer -> Capacity
 getCapacity = bbCapacity
 {-# INLINE getCapacity #-}
 
-readLimit :: ByteBuffer -> IO Int
+readLimit :: ByteBuffer -> IO Limit
 readLimit = readIORef . bbLimit
 {-# INLINE readLimit #-}
 
-writeLimit :: ByteBuffer -> Int -> IO ()
+writeLimit :: ByteBuffer -> Limit -> IO ()
 writeLimit bb = writeIORef (bbLimit bb)
 {-# INLINE writeLimit #-}
 
-readPosition :: ByteBuffer -> IO Int
+readPosition :: ByteBuffer -> IO Position
 readPosition = readIORef . bbPosition
 {-# INLINE readPosition #-}
 
-writePosition :: ByteBuffer -> Int -> IO ()
+writePosition :: ByteBuffer -> Position -> IO ()
 writePosition bb = writeIORef (bbPosition bb)
 {-# INLINE writePosition #-}
 
 incrPosition :: ByteBuffer -> Int -> IO ()
-incrPosition bb i = modifyIORef (bbPosition bb) (+ i)
+incrPosition bb i = modifyIORef (bbPosition bb) (+ fromIntegral i)
 {-# INLINE incrPosition #-}
 
-readMark :: ByteBuffer -> IO Int
+readMark :: ByteBuffer -> IO Position
 readMark = readIORef . bbMark
 {-# INLINE readMark #-}
 
-writeMark :: ByteBuffer -> Int -> IO ()
+writeMark :: ByteBuffer -> Position -> IO ()
 writeMark bb = writeIORef (bbMark bb)
 {-# INLINE writeMark #-}
 
+readSlice :: ByteBuffer -> IO Slice
+readSlice = readIORef . bbSlice
+
+writeSlice :: ByteBuffer -> Slice -> IO ()
+writeSlice bb = writeIORef (bbSlice bb)
+
 ------------------------------------------------------------------------
 
 remaining :: ByteBuffer -> IO Int
 remaining bb = do
   lim <- readLimit bb
   pos <- readPosition bb
-  return (lim - pos)
+  return (fromIntegral (lim - fromIntegral pos))
 
 ------------------------------------------------------------------------
 -- * Checks
@@ -87,23 +118,23 @@ invariant bb = do
   lim  <- readLimit bb
   let capa = getCapacity bb
   assert ((mark == (-1) || 0 <= mark) &&
-          mark <= pos &&
-          pos <= lim &&
-          lim <= capa)
+          mark <= fromIntegral pos &&
+          pos <= fromIntegral lim &&
+          lim <= fromIntegral capa)
     (return ())
 
 ------------------------------------------------------------------------
 -- * Create
 
 allocate :: Int -> IO ByteBuffer
-allocate capa = do
-  Ptr addr# <- mallocBytes capa
-  newByteBuffer addr# capa capa 0
+allocate capa@(I# capa#) = IO $ \s ->
+  case newPinnedByteArray# capa# s of
+    (# s', mba# #) -> unIO (newByteBuffer mba# (Capacity capa) (Limit capa) 0 Nothing) s'
 
 allocateAligned :: Int -> Int -> IO ByteBuffer
-allocateAligned capa align = do
-  Ptr addr# <- posixMemalign capa align
-  newByteBuffer addr# capa capa 0
+allocateAligned capa@(I# capa#) align@(I# align#) = IO $ \s ->
+  case newAlignedPinnedByteArray# capa# align# s of
+    (# s', mba# #) -> unIO (newByteBuffer mba# (Capacity capa) (Limit capa) 0 Nothing) s'
 
 mmapped :: FilePath -> Int -> IO ByteBuffer
 mmapped fp capa = do
@@ -116,52 +147,56 @@ mmapped fp capa = do
   return bb
 
 wrap :: ByteBuffer -> IO ByteBuffer
-wrap bb = newByteBuffer (bbAddr bb) size size 0
+wrap bb = newByteBuffer (bbData bb) capa lim (Position 0) (Just (bbSlice bb))
   where
-    size = bbCapacity bb
+    capa = bbCapacity bb
+    lim  = Limit (fromIntegral capa)
 
 wrapPart :: ByteBuffer -> Int -> Int -> IO ByteBuffer
-wrapPart bb offset len = newByteBuffer (bbAddr bb) size (offset + len) offset
+wrapPart bb offset len = newByteBuffer (bbData bb) capa lim pos (Just (bbSlice bb))
   where
-    size  = bbCapacity bb
+    capa = bbCapacity bb
+    lim  = Limit (fromIntegral offset + fromIntegral len)
+    pos  = Position (fromIntegral offset)
 
 slice :: ByteBuffer -> IO ByteBuffer
 slice bb = do
-  I# pos# <- readPosition bb
+  pos <- readPosition bb
   left <- remaining bb
-  newByteBuffer (bbAddr bb `plusAddr#` pos#) left left 0
+  slice <- newIORef (fromIntegral pos)
+  newByteBuffer (bbData bb) (Capacity left) (Limit left) (Position 0) (Just slice)
 
 duplicate :: ByteBuffer -> IO ByteBuffer
 duplicate bb = do
   lim <- readLimit bb
   pos <- readPosition bb
-  newByteBuffer (bbAddr bb) (getCapacity bb) lim pos
+  newByteBuffer (bbData bb) (getCapacity bb) lim pos (Just (bbSlice bb))
 
 ------------------------------------------------------------------------
 
+mark :: ByteBuffer -> IO ()
+mark bb = do
+  pos <- readPosition bb
+  writeMark bb pos
+
 compact :: ByteBuffer -> IO ByteBuffer
 compact = undefined
 
 ------------------------------------------------------------------------
 
--- | The position is set to zero, the limit is set to the capacity, and the mark
--- is discarded.
 clear :: ByteBuffer
 clear = undefined
 
--- | The limit is set to the current position and then the position is set to
--- zero. If the mark is defined then it is discarded.
 flipBB :: ByteBuffer -> IO ByteBuffer
 flipBB = undefined
 
--- | Rewinds this buffer. The position is set to zero and the mark is discarded.
 rewind :: ByteBuffer -> IO ByteBuffer
 rewind = undefined
 
--- | Resets this buffer's position to the previously-marked position.
--- Invoking this method neither changes nor discards the mark's value.
-reset :: ByteBuffer
-reset = undefined
+reset :: ByteBuffer -> IO ()
+reset bb = do
+  mrk <- readMark bb
+  writePosition bb mrk
 
 ------------------------------------------------------------------------
 -- * Single-byte relative and absolute operations
@@ -235,6 +270,8 @@ getStorableAt bb ix = do
 -- indexWord32OffAddr#
 -- indexWord64OffAddr#
 
+-- writeIntArray#
+
 ------------------------------------------------------------------------
 -- * Mapped
 
diff --git a/src/journal/src/Journal/Internal/Metrics.hs b/src/journal/src/Journal/Internal/Metrics.hs
index df574c3c..51cba42c 100644
--- a/src/journal/src/Journal/Internal/Metrics.hs
+++ b/src/journal/src/Journal/Internal/Metrics.hs
@@ -12,11 +12,13 @@ import GHC.ForeignPtr
 import GHC.Prim
 import GHC.Types
 
+import Journal.Internal.ByteBuffer
+
 ------------------------------------------------------------------------
 
 data Metrics a = Metrics
-  { mPtr     :: ForeignPtr Word8
-  , mOffsets :: Vector Int
+  { mMetadata :: ByteBuffer
+  , mBuffer   :: ByteBuffer
   }
 
 newtype MetricsSchema a = MetricsSchema
@@ -26,16 +28,13 @@ newtype MetricsSchema a = MetricsSchema
 data MetricsType = Counter | Histogram
 
 newMetrics :: (Enum a, Bounded a) => MetricsSchema a -> FilePath -> IO (Metrics a)
-newMetrics ms@(MetricsSchema xs) fp = IO $ \s ->
-  -- XXX: just use mallocForeignPtrBytes :: Int -> IO (ForeignPtr a)
-  -- XXX: Aligned to avoid possible false sharing?
-  case newPinnedByteArray# len s of
-    (# s', arr #) -> case byteArrayContents# (unsafeCoerce# arr) of
-      addr# -> (# s', Metrics (ForeignPtr addr# (PlainPtr arr)) (calculateOffsets ms) #)
-  -- ptr' <- mmap ptr ...
-  -- assertM (ptr' == ptr)
+newMetrics ms@(MetricsSchema xs) fp = do
+  bb <- mmapped fp (sizeOfOffsets + sizeOfMetrics ms)
+  meta <- wrapPart bb 0 sizeOfOffsets
+  buf  <- wrapPart bb (sizeOfOffsets + 1) (sizeOfOffsets + sizeOfMetrics ms)
+  return (Metrics meta buf)
   where
-    I# len = length xs
+    sizeOfOffsets = length xs * sizeOf (8 :: Int)
 
 -- XXX: how can we avoid `incrCounter` being called on a histogram?
 incrCounter :: (Enum a, Bounded a) => Metrics a -> a -> Int -> IO ()
@@ -54,7 +53,7 @@ validSchema :: (Enum a, Bounded a) => MetricsSchema a -> Either SchemaError ()
 validSchema = undefined -- map (fromEnum . fst) . unMetricsSchema
 
 lookupOffset :: (Enum a, Bounded a) => Metrics a -> a -> Int
-lookupOffset m x = mOffsets m Vector.! fromEnum x
+lookupOffset m x = undefined -- mOffsets m Vector.! fromEnum x
 
 calculateOffsets :: (Enum a, Bounded a) => MetricsSchema a -> Vector Int
 calculateOffsets (MetricsSchema xs)
@@ -62,13 +61,26 @@ calculateOffsets (MetricsSchema xs)
   . Vector.fromList
   . scanl (\ih (_, mty) -> intsOfSpaceNeeded mty + ih) 0
   $ xs
-  where
-    intsOfSpaceNeeded :: MetricsType -> Int
-    intsOfSpaceNeeded Counter = 1 -- count
-    intsOfSpaceNeeded Histogram
-      = 2 ^ 16 -- buckets
-      + 1      -- sum
-      + 1      -- count
+
+intsOfSpaceNeeded :: MetricsType -> Int
+intsOfSpaceNeeded Counter = 1 -- count
+intsOfSpaceNeeded Histogram
+  = 2 ^ 16 -- buckets
+  + 1      -- sum
+  + 1      -- count
+
+sizeOfMetrics :: MetricsSchema a -> Int
+sizeOfMetrics
+  = (* sizeOf (8 :: Int))
+  . sum
+  . map (intsOfSpaceNeeded . snd)
+  . unMetricsSchema
+
+addNewCounter :: ByteBuffer -> IO ()
+addNewCounter bb = undefined
+
+addNewHistogram :: ByteBuffer -> IO ()
+addNewHistogram = undefined
 
 ------------------------------------------------------------------------
 
diff --git a/src/journal/src/Journal/Internal/Mmap.hs b/src/journal/src/Journal/Internal/Mmap.hs
index e0903b37..a5dce8f3 100644
--- a/src/journal/src/Journal/Internal/Mmap.hs
+++ b/src/journal/src/Journal/Internal/Mmap.hs
@@ -120,14 +120,15 @@ posixMemalign align size = do
   peek memPtr
 
 sysconfPageSize :: IO Int
-sysconfPageSize = fromIntegral <$> c_sysconf 30
+sysconfPageSize = fromIntegral <$> c_sysconf _SC_PAGE_SIZE
+  where
+    _SC_PAGE_SIZE = 30
 
 ------------------------------------------------------------------------
 
-  {-
 main :: IO ()
 main = do
-  fptr <- posixMemalign 4096 4096
+  fptr <- posixMemalignFPtr 4096 4096
   withForeignPtr fptr $ \ptr' -> do
     ptr <- mmap (Just ptr') 16 (PROT (READ :| WRITE)) MAP_SHARED Nothing 0
     if ptr /= ptr'
@@ -135,5 +136,3 @@ main = do
     else do
       msync ptr 16 MS_SYNC False
       munmap ptr 16
-
--}