diff --git a/storage.py b/storage.py
index b6d8219..215ccf6 100644
--- a/storage.py
+++ b/storage.py
@@ -55,7 +55,7 @@ def dictToH5Group(d,group,link_copy=True):
     if isinstance(value,(list,tuple)): value = np.asarray(value)
     if isinstance(value,dict):
       group.create_group(key)
-      dictToH5Group(value,group[key])
+      dictToH5Group(value,group[key],link_copy=link_copy)
     elif value is None:
       group[key] = "NONE_PYTHON_OBJECT"
     elif isinstance(value,np.ndarray):
@@ -65,22 +65,22 @@ def dictToH5Group(d,group,link_copy=True):
       elif isinstance(value,np.ndarray) and value.ndim == 1 and isinstance(value[0],np.ndarray):
         group.create_group(key)
         group[key].attrs["IS_LIST_OF_ARRAYS"] = True
-        for index,array in enumerate(value): dictToH5Group( { "index%010d"%index : array},group[key] );
+        for index,array in enumerate(value): dictToH5Group( { "index%010d"%index : array},group[key],link_copy=link_copy );
         TOTRY = False; # don't even try to save as generic call group[key]=value
-      else:
-        if link_copy:
-          found_address = None
-          for address,(file_handle,array) in _array_cache.items():
-            if np.array_equal(array,value) and group.file == file_handle:
-              log.info("Found array in cache, asked for %s/%s, found as %s"%(group.name,key,address))
-              found_address = address
-            if found_address is not None:
-              value = group.file[found_address]
+      if link_copy:
+        found_address = None
+        for address,(file_handle,array) in _array_cache.items():
+          if np.array_equal(array,value) and group.file == file_handle:
+            log.info("Found array in cache, asked for %s/%s, found as %s"%(group.name,key,address))
+            found_address = address
+            break
+        if found_address is not None:
+          value = group.file[found_address]
       try:
         if TOTRY:
           group[key] = value
           if link_copy:
-            log.info("Addind array %s to cache"%(group.name))
+            log.info("Addind array %s to cache"%(group[key].name))
             _array_cache[ group[key].name ] = (group.file,value)
       except Exception as e:
         log.warning("Can't save %s, error was %s"%(key,e))
@@ -92,13 +92,13 @@ def dictToH5Group(d,group,link_copy=True):
         log.error("Can't save %s, error was %s"%(key,e))
  
 
-def dictToH5(h5,d):
+def dictToH5(h5,d,link_copy=False):
   """ Save a dictionary into an hdf5 file
       TODO: add capability of saving list of array
       h5py is not capable of handling dictionaries natively"""
   h5 = h5py.File(h5,mode="w")
 #  group = h5.create_group("/")
-  dictToH5Group(d,h5["/"])
+  dictToH5Group(d,h5["/"],link_copy=link_copy)
   h5.close()
 
 def h5ToDict(h5,readH5pyDataset=True):
@@ -161,7 +161,7 @@ def save(fname,d,link_copy=True):
     if extension == ".npz": 
       return dictToNpz(fname,d)
     elif extension == ".h5":
-      return dictToH5(fname,d)
+      return dictToH5(fname,d,link_copy=link_copy)
     elif extension == ".npy":
       return dictToNpy(fname,d)
     else:
@@ -286,7 +286,13 @@ class DataStorage(dict):
     keys = [k for k in keys if k[0] != '_' ]
     return keys
 
-  def save(self,fname=None,link_copy=True):
+  def save(self,fname=None,link_copy=False):
+    """ link_copy: only works in hfd5 format
+        save space by creating link when identical arrays are found,
+        it slows down the saving (3 or 4 folds) but saves A LOT of space
+        when saving different dataset together (since it does not duplicate
+        internal pyfai matrices
+    """
     if fname is None: fname = self.filename
     assert fname is not None
     save(fname,self,link_copy=link_copy)