anchor.diff:  % cache. It doesn't harm to have a long interval).
   -define(TAG_CACHE_INTERVAL, 10 * ?MINUTE).
   
  +% Tag cache expires in this many milliseconds if tag can't be fetched
  +-define(TAG_EXPIRES_ONERROR, 1 * ?SECOND).
  +
  +% How often node should refresh its tag cache from disk
  +-define(FIND_TAGS_INTERVAL, ?DAY).
  +
   % How often buffered (delayed) updates need to be flushed. Tradeoff: The
   % longer the interval, the more updates are bundled in a single commit.
   % On the other hand, in the worst case the requester has to wait for the
  
positive.code: 
  % Interval for checking available disk space in ddfs_node
  -define(DISKSPACE_INTERVAL, 10 * ?SECOND).
  
  % How often node should refresh its tag cache from disk
  -define(FIND_TAGS_INTERVAL, ?DAY).
  
  % /dfs/tag/ requests can be ?MAX_TAG_BODY_SIZE bytes at most
  -define(MAX_TAG_BODY_SIZE, (512 * ?MB)).
  
negative.code: % estimated time to traverse all the volumes on a DDFS node.
  -define(GC_PROGRESS_INTERVAL, 30 * ?MINUTE).
  
  % Number of extra replicas (i.e. lost replicas recovered during GC) to
  % allow before deleting extra replicas.
  -define(NUM_EXTRA_REPLICAS, 1).
  