Patent ID: 7747583

Claim:
A method by which a disk-based data storage system attached to a network is organized for protecting historical records of stored data entities, wherein storage clients can increase the level of protection but not reduce it, the method comprising: recording distinct states of the stored data entities, corresponding to different moments of time, as a plurality of entity versions coexisting within the data storage system; designating at least some of the plurality of entity versions as historical versions; and assigning a finite expiration time to an entity version that is one of the historical versions, before which time both modification and deletion are prohibited and after which time deletion is allowed; wherein the assigning is done by the disk-based data storage system, in response to a request communicated to it over the network by a client program; wherein, after the expiration time has been assigned and before the expiration time has passed, the client program requests that the expiration time be set to a specified later time and it is changed to the later time; wherein, after the expiration time has been assigned and before the expiration time has passed, the client program requests that the expiration time be set to a specified earlier time and the request is denied and the expiration time is not changed; and wherein, once the expiration time has been assigned and as long as the expiration time has not yet passed, the client program can change the expiration time to later times but cannot cause the disk-based data storage system to change the expiration time to an earlier time, nor can the client program cause the entity version to be deleted from the disk-based data storage system at an earlier time than the expiration time.