A disaster-recovery system contains a networked array of synchronous-to-asynchronous converter (SATC) modules that connect source databases to target backup databases. During backup, the system replicates each source-database transaction through a chain of these SATCs to a corresponding target, storing a local copy of the transaction on each SATC along the way. Each transaction's path between its source-target pair is identified by a set of tracking entries, where each entry identifies one SATC in the path. Every backup transfer between two SATCs in a chain is performed synchronously, such that a successor SATC confirms a successful transfer to a predecessor SATC only after the successor can confirm a successful transfer to the next SATC in the chain. During a subsequent recovery operation, tracking entries are regenerated to locate locally stored transactions that had not time to be fully replicated before a catastrophic failure had occurred.