Data being replicated from site A to site B using disk buffering to create extended distance consistent point in time copies every hour. In the event of a site failure at A, what is the maximum amount of data that will be missing at site B?

With hourly replication from site A to site B, the maximum data loss depends on when failure occurs relative to the replication cycle. If site A fails immediately after a successful replication, site B loses 0 hours of data (just the data from the current uncompleted hour). If site A fails immediately before the next replication, site B loses the entire current hour's data plus potentially the previous hour if replication was delayed. The worst case is approximately 2 hours - the current incomplete hour plus the previous hour's data that hasn't been fully transferred yet.