add DN storage to a BlockInfo will not replace the different storage from same DN

removeStorage(getStorageInfo(idx));

1 boolean addStorage(DatanodeStorageInfo storage) {
2   boolean added = true;
3    int idx = findDatanode(storage.getDatanodeDescriptor());
4   if(idx >= 0) {
5      if (getStorageInfo(idx) == storage) { // the storage is already there
6        return false;
7      } else {
8        // The block is on the DN but belongs to a different storage.
9        // Update our state.
10        removeStorage(storage);
11        added = false;      // Just updating storage. Return false.
12     }
13  }
14  // find the last null node
15  int lastNode = ensureCapacity(1);
16  setStorageInfo(lastNode, storage);
17  setNext(lastNode, null);
18  setPrevious(lastNode, null);
19  return added;
20}