This paper examines the problem of comparing large replicated files in a context in which communication dominates the cost of comparison. A low-cost checking matrix is proposed for comparison of these replicated files. The checking matrix is composed of check symbols generated by a divide-and-conquer encoding algorithm. The matrix allows for detection and diagnosis of disagreeing pages with very little communication overhead. In contrast to a previous O(N) proposal, the storage requirement for the checking matrix is O(log N), where N is the number of pages in the file. The matrix can be stored in main memory without the need for extra accesses to disk during normal updates of pages.