anchor.diff:          {ok, true} ->
               ok;
           {ok, false} ->
  -            {ok, _} = datastore_model:create(?CTX, new_doc(SpaceId, StorageId)),
  -            ok;
  +            case datastore_model:create(?CTX, new_doc(SpaceId, StorageId)) of
  +                {ok, _} -> ok;
  +                {error, already_exists} -> ok
  +            end;
           Error  ->
               ?error("Failed to check if storage_sync_monitoring document for space ~p and storage ~p exists due to ~p",
                   [SpaceId, StorageId, Error])
  
positive.code: %%-------------------------------------------------------------------
  %% @doc
  %% Prepares document for new update scan.
  %% It resets control counters, and increases to_process counter and
  %% queue_length histograms by 1.
  %% This function also sets scan start_time.
  
negative.code: 
  %%-------------------------------------------------------------------
  %% @doc
  %% Prepares existing document for new import scan.
  %% This function assumes that document has already been created by
  %% ?MODULE:ensure_created/2 function.
  %% It resets control counters, and increases to_process counter and
  %% queue_length histograms by 1.
  %% This function also sets scan start_time.
  