Current cluster architectures provide the ideal environment to run federations of main-memory database systems (FMMDBs). In FMMDBs, data resides in the main memory of the federation servers. FMMDBs significantly improve performance by avoiding I/O during the execution of read operations. To maximize the performance of update transactions as well, some applications recur to deferred disk writes. This means that update transactions commit before their modifications are written on stable storage and durability must be ensured outside the database. While deferred disk writes in centralized MMDBs relax the durability property of transactions only, in FMMDBs transaction atomicity may be also violated in case of failures. We address this issue from the perspective of log-based rollback-recovery in distributed systems and provide an efficient solution to the problem. Besides presenting a mechanism to ensure atomicity in FMMDBs, the paper bridges the gap between rollback-recovery in message-passing distributed systems and distributed transaction processing, and shows how results developed in the first context can be exploited in the second.