A memory system (1, 11) comprising a network (2, 12) of logically-connected memory components each comprising an individual memory-address space, wherein: the memory-address spaces of the individual memory components are aggregated and exposed as a single memory component to components external to the memory system (1, 11) seeking to write or read data objects in the memory system (1, 11); and the memory system (1, 11) is configured to implement a lazy data replication protocol to hold plural replicas of data objects in the memory system; characterized by the memory system (1, 11) comprising: a receiving module to receive requests to update data objects in the memory system; and an update-synchronization manager; wherein the memory system (1, 11) is configured to implement a data-replication protocol in which: for data objects written to the memory system (1, 11), a primary replica of the respective data object is written in a first memory component and each of a selected number of other replicas of said data object is written in a respective second memory component; and responsive to an update request to update a data object held in the memory system (1, 11): - the first memory component updates the primary replica of said data object and notifies the update-synchronization manager that the respective update of said data object has been implemented on the primary replica, - the update-synchronization manager transmits, to the second memory component(s) of said memory system (1, 11), update instructions indicative of respective updates that have been implemented on the primary replica, the transmitted update instructions being ordered according to the order of implementation of the respective updates on the primary replica; and - responsive to reception of update instructions, the second memory components update the respective other replicas of the data object in the same order that updates are implemented on the primary replica. the memory-address spaces of the individual memory components are aggregated and exposed as a single memory component to components external to the memory system (1, 11) seeking to write or read data objects in the memory system (1, 11); and the memory system (1, 11) is configured to implement a lazy data replication protocol to hold plural replicas of data objects in the memory system; characterized by the memory system (1, 11) comprising: a receiving module to receive requests to update data objects in the memory system; and an update-synchronization manager; wherein the memory system (1, 11) is configured to implement a data-replication protocol in which: for data objects written to the memory system (1, 11), a primary replica of the respective data object is written in a first memory component and each of a selected number of other replicas of said data object is written in a respective second memory component; and responsive to an update request to update a data object held in the memory system (1, 11): - the first memory component updates the primary replica of said data object and notifies the update-synchronization manager that the respective update of said data object has been implemented on the primary replica, - the update-synchronization manager transmits, to the second memory component(s) of said memory system (1, 11), update instructions indicative of respective updates that have been implemented on the primary replica, the transmitted update instructions being ordered according to the order of implementation of the respective updates on the primary replica; and - responsive to reception of update instructions, the second memory components update the respective other replicas of the data object in the same order that updates are implemented on the primary replica. for data objects written to the memory system (1, 11), a primary replica of the respective data object is written in a first memory component and each of a selected number of other replicas of said data object is written in a respective second memory component; and responsive to an update request to update a data object held in the memory system (1, 11): - the first memory component updates the primary replica of said data object and notifies the update-synchronization manager that the respective update of said data object has been implemented on the primary replica, - the update-synchronization manager transmits, to the second memory component(s) of said memory system (1, 11), update instructions indicative of respective updates that have been implemented on the primary replica, the transmitted update instructions being ordered according to the order of implementation of the respective updates on the primary replica; and - responsive to reception of update instructions, the second memory components update the respective other replicas of the data object in the same order that updates are implemented on the primary replica. - the first memory component updates the primary replica of said data object and notifies the update-synchronization manager that the respective update of said data object has been implemented on the primary replica, - the update-synchronization manager transmits, to the second memory component(s) of said memory system (1, 11), update instructions indicative of respective updates that have been implemented on the primary replica, the transmitted update instructions being ordered according to the order of implementation of the respective updates on the primary replica; and - responsive to reception of update instructions, the second memory components update the respective other replicas of the data object in the same order that updates are implemented on the primary replica.