The present disclosure generally relates to creating virtualized block storage devices whose data is replicated across isolated computing systems to lower risk of data loss even in wide-scale events, such as natural disasters. The virtualized device can include at least two volumes, each of which is implemented in a distinct computing system. Due to separation between volumes, replication lag may occur, in which data persisted to a first volume is not immediately persisted to a second volume. Such lag can increase a potential for data loss in the event that the first volume fails. Embodiments of the present disclosure relate to managing data loss risk by determining an expected maximum difference between the data stored at the two volumes, in a manner that does not require decrypting the data written to the volumes or perfect knowledge of the state of the distributed system at a single point.