Patent ID: 7478096
Filing Date: 2009-01-13
Classification: G06F,Y10S

Abstract:
1. A method by which a disk-based distributed data storage system is organized for protecting historical records of stored data entities, the method comprising: recording distinct states of entities, corresponding to different moments of time, as separate entity versions coexisting within the disk-based distributed data storage system; storing an entity version in the disk-based distributed data storage system, with a copy of the entity version located at each of a plurality of storage sites; and assigning expiration times to the entity version, with separate expiration times assigned at each of the plurality of storage sites according to a shared set of rules, before which times both modification and deletion of the entity version are prohibited, and after which times it is deleted from the disk-based distributed data storage system; wherein a storage client communicating with the disk-based distributed data storage system deposits the entity version into the storage system and later retrieves it; wherein an action taken by the storage client communicating with the disk-based distributed data storage system causes an expiration time, which is one of the separate expiration times, to be assigned to the entity version; wherein no subsequent action that the storage client communicating with the disk-based distributed data storage system can take will cause the expiration time to be changed to an earlier time; wherein a request communicated by the storage client to the disk-based distributed data storage system, which would cause or allow the entity version to be deleted from the disk-based distributed data storage system before the expiration time, is denied; and wherein no alteration or corruption of expiration times assigned at any single storage site that is a part of the disk-based distributed data storage system will allow the entity version to be deleted from all of the plurality of storage sites before the assigned expiration times.