multi-frag in cache

[张练]

I'm considering the multi fragment issue. In iocore/cache/CacheWrite.cc,
function CacheVC::openWriteMain, there are phrases :
  if (length > target_fragment_size() &&
      (length < target_fragment_size() + target_fragment_size() / 4))
    write_len = target_fragment_size();
  else
    write_len = length;

I want to know why it does like that?
If one object's size is between [target_fragment_size() +
target_fragment_size() / 4, MAX_FRAG_SIZE) , then does multi fragments
happen?

-- 
Best regards,
mohan_zl