Good Post by Erwin van Londen (thank you)
So this week I had an interesting case. As you know the Hitachi arrays have a replication functionality called HUR (Hitachi Universal Replicator) which is an advanced asynchronous replication solution offered for Mainframe and OpenSystems environments. HUR does not use a primary to secondary push method but rather the target system is issuing reads to the primary array after which this one sends the required data. This optimizes the traffic pattern by using batches of data. From a connectivity perspective you will mostly see full 2K FC frames which means on long distance connections (30KM to 100KM) you can very effectively keep a fairly low number of buffer-credits on both sides whilst still maintain optimum link utilization.
Read on here