An efficient data storage system is described. An agent software application on computing devices in a first tier processes snapshot backups and pushes them to an appliance software application on a server in a second tier. The appliance software application processes archive backups and pushes them to cloud storage in a third tier. A cloud application on a management server receives storage policy specifications from customers and promulgates the policies to the agent software application and the appliance software application. The policy specifications include time periods and retention set information for the backups. When a retention set has been exceeded, the storage system is pruned to remove file references to unneeded files and delete data files no longer referenced in storage sets in the retention set.