Comparing multiple file copies using minimal communication

The minimum amount of communication necessary to identify any given number of erroneous pages among the copies of a file is determined and a technique to attain this minimum is presented. We study the general case of identifying all corrupted pager among any number of secondary sites. We assume that secondary sites can communicate only with the primary site. We present a protocol that identifies the corrupted pages and prove that this protocol is optimal in the sense of requiring the minimum amount of communication. This protocol relies on the structure of Reed-Solomon codes.<>