Server most certainly can rely on client to store a redundant copy of the data, as there are ways to ensure the data authenticity. Should the server fail and ge

Server most certainly can rely on client to store a redundant copy of the data, as there are ways to ensure the data authenticity. Should the server fail and get restored from an hour-old backup, the last hour worth of changes can be fetched from the client, after data integrity verification. Thus the server could get away with hourly backup instead of every-five-second, or full-blown database mirroring.