Data backup copying with delayed directory updating and reduced numbers of DASD accesses at a back up site using a log structured array data storage

• US 5,555,371 A
• Filed: 07/18/1994
• Issued: 09/10/1996
• Est. Priority Date: 12/17/1992
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Micka, William Frank, Shomler, Robert Wesley, Duyanovich, Linda Marie
• Primary Examiner(s): Beausoliel, Jr., Robert W.
• Assistant Examiner(s): CHUNG, PHUNG M
• Application Number:
  US08/276,379
• Time in Patent Office: 785 Days
• Field of Search: 395/575, 395/425, 395/182.11, 395/489, 371/40.1, 371/61, 371/62, 371/2.1, 371/2.2, 371/10.1
• US Class Current: 714/13
• CPC Class Codes: G06F 11/2064 while ensuring consistency
• CPC Class Codes: G06F 11/2066 Optimisation of the communication load
• CPC Class Codes: G06F 11/2074 Asynchronous techniques
• CPC Class Codes: G06F 11/2082 Data synchronisation
• CPC Class Codes: G11C 29/74 using duplex memories, i.e. using dual copies
• CPC Class Codes: H04L 67/1095 Replication or mirroring of data, e.g. scheduling or transport for data synchronisation between network nodes
• CPC Class Codes: H04L 69/40 for recovering from a failure of a protocol instance or entity, e.g. service redundancy protocols, protocol state redundancy or protocol service redirection management of faults, events, alarms or notifications in data switching networks H04L41/06

Abstract

Primary and secondary data processing systems are coupled via a communication system. Data storage in both systems is provided by a log structured array (LSA) system that stores data in compressed form. Each time data are updated within LSA, the updated data are stored in a data storage location different from the original data. Selected data recorded in a primary data storage of the primary system is remote dual copied to the secondary system for congruent storage in a secondary data storage, such as for disaster recovery purposes. The primary systems creates a remote copying session. Within such remote copying session, a series of "pending write update" sessions are ESTABLISHED. All data updated within each pending write update session is a consistency group of data. Within each pending write update session update data are retentively stored in both the primary and secondary systems (such as in a non-volatile cache). Addressability of such update data within a pending write update session is through separate pending write directories. The main (primary and secondary) directory for data is not updated such that all original (not updated) data are addressable. A COMMIT command terminates each pending write update session. Congruence of the sequence of updating in the primary system is maintained in the secondary system updating procedure.

Claims

1. A dual mode remote data copy apparatus for transferring updated data from a primary data-storage system to a secondary data-storage system, including in combination:

a primary data processing system connected to said primary data-storage system;

said secondary data-storage system connected to said primary data-storage system and to said primary data processing system;

said primary and secondary data-storage systems having primary and secondary long-term storage comprising first and second peripheral means, respectively;

each said peripheral means in both said data-storage systems having a plurality of first and second device addressable data-storage locations for retentively storing data;

primary and secondary directories respectively in said primary and secondary data-storage systems for respectively providing addressability of data stored in said first and second peripheral means;

an update directory in said secondary data-storage system for providing addressability of update copy data stored in said second peripheral means;

pending write update means in said primary data processing system and being connected to said primary and secondary data-storage systems for establishing a pending write update session wherein during said pending write update session predetermined data contained in predetermined ones of addressable data units stored in said primary data-storage system are updated by one or more successive copies of said update data, each said copy of each said updated addressable data unit is copied to said secondary data-storage system and wherein said primary directory is updated to address each successive copy of said update data but said secondary directory is not updated until said pending write update session is terminated, then updated with a most recent copy of said update data for the respective addressable data units;

primary data update means in said primary data-storage system and connected to said pending write update means and to said primary data processing system for repeatedly receiving copies of said update data from said primary data processing system during said pending write update session and for responding to receiving said update data during said pending write update session for repeatedly storing said update data in said first peripheral means as successive copies of said addressable data units, respectively, that are updates to data of said addressable data units currently stored in said first peripheral means and updating said primary directory to address said update data, as copied data, stored in said primary data-storage system such that said primary directory has only addresses for a last recorded copy of data that are updated a plurality of times;

time means in said primary data update means for indicating a time of updating for each said data update;

identifying data updated at each indicated time of updating for indicating which data are most recently updated copy of said update data;

system inter-communication means connected to said primary and secondary data-storage systems;

to said pending write update means;

said time indicating means and being responsive to said pending write update means establishing said pending write update session; and

to said first update means updating data stored in said first peripheral means in a primary temporary data storage, as a part of said pending write update session, said update data stored in said primary data-storage system, to copy each respective said time of updating indication and said identification to said secondary data-storage system and for indicating to said secondary data-storage system that said copied update data, said time of updating indication and said identification of data are a part of said pending write update session;

secondary data update means in said secondary data-storage system connected to said update directory, to said primary temporary data storage and to said system inter-communication means for responding to receiving said update data, said time of storage indication and identification of said update data in said pending write update session for storing said update data in said second peripheral means and to update said update directory including storing said time of updating indication and identification of said update data in said update directory for indicating said received update data are a part of said predetermined data;

consistency means in said primary data processing system for indicating termination of said pending write update session and that said secondary directory is now to be updated for actuating secondary data-storage systems to update said secondary directory; and

secondary directory update means being connected to said consistency means and having data selection means for selecting only that portion of said copied update data stored in said second means and having a time of updating indication that indicates which of said copied update data is a most recent copy of said copied update data and for updating said secondary directory to indicate addresses of only said most recent copy of said copied update data currently stored in said second peripheral means.

2. The apparatus set forth in claim 1, further including, in combination:

said first peripheral means having a plurality of addressable first data storage devices, each of said addressable first data storage devices having a plurality of said addressable data-storage locations;

time stamp means in said primary data processing system for generating a current time indication;

said time means being connected to said time stamp means for receiving said current time indication for making a copy of said received current time indication for each of said updates of said updated data stored in said primary data-storage system;

said system inter-communication means sending each said stored time of updating indication with the respective copied update data to said secondary data-storage system;

said update directory being connected to said system inter-communication means and to said secondary directory update means for receiving and storing each said copied time of updating indication and said identification of said copied update data received from said primary data-storage system at the time indicated in said received time of updating indication, respectively;

said secondary directory update means responding to said termination of said pending write update session to access said update directory to retrieve and sort the time of updating indications in order of time for selecting a most recent time of updating indication for each said identified data having plural copies in said second peripheral means each with a different time of updating indication for creating a set of said most recent copy of said copied updated data, then updating said secondary directory.

3. The apparatus set forth in claim 2, further including, in combination:

plural subsystem means in said primary data storage connected to said first peripheral means and to said primary data processing system and having a plurality of first subsystems for independently connecting all of said first addressable data storage devices to said primary data processing system such that said first data storage devices and said primary temporary data storage can access any one of said first subsystems;

first subsystem indicating means in said primary data update means having a predetermined set of sequence numbers for allocating and sending a subset of said sequence numbers to respective ones of said first subsystems;

said primary data update means being connected to said first subsystem indicating means for assigning one of said sequence numbers to each of said data updates, respectively, for indicating which of said first subsystems transferred said data updates to said first peripheral means;

said system inter-communication means adding each of said assigned sequence numbers to the respective update data being copied to said secondary data-storage system; and

said secondary directory update means further selecting said time of updating indications that are also identified by said sequence numbers, then sorting said time of updating indications for each identified data, then sorting the time of updating indications for selecting the most recent time of updating indication for each said identified data to select data that comprises said most recent copy, respectively.

4. The apparatus set forth in claim 3, further including, in combination:

said secondary data-storage system comprising a log structured array; and

said log structured array having N addressable second data storage devices, N being a positive integer, each of said arrays being divided into a plurality of addressable data-storing segments, each of said plurality of segments consisting of a column segment in each of said second data storage devices, respectively, wherein addresses of said column segments in any of said N addressable second data storage devices having identical addresses within the respective N data storage devices.

5. The apparatus set forth in claim 4, further including, in combination:

said log structured array having data compression means for compressing all data stored in the respective addressable data storage devices; and

said secondary directory update means updating said log structured array including writing updated data and all non-updated original data in a new addressable area of the respective log structured array, then updating said secondary directory to indicate only said new addressable data.

6. The apparatus set forth in claim 5, further including, in combination:

said consistency means being in said primary data processing system;

said consistency means having end means for indicating that all data updates to said primary data-storage system have been completed; and

said consistency means responding to said end means for indicating said termination of said pending write update session.

7. The apparatus set forth in claim 5, further including, in combination:

said log structured array having storing means connected to said compression means for combining diverse compressed data into a compressed file for storage in said second device at predetermined ones of said second device addressable data-storage locations, respectively, and indicating said predetermined ones of said second device addressable data-storage locations; and

said secondary data update means being connected to said storing means for receiving said indications of said addressable storage area storing said copied predetermined data for updating said update directory.

8. The apparatus set forth in claim 7, further including, in combination:

said secondary data-storage system including a non-volatile random access control memory; and

said secondary directory being stored in said non-volatile random access control memory in said secondary data-storage system.

9. The apparatus as set forth in claim 7, further including, in combination:

a secondary data processing system located physically remote from said primary data processing system;

said secondary data-storage system being in said secondary data processing system;

first and second data communications means respectively in said primary and secondary data processing systems and being connected to said system inter-communication means for transferring said update data from said primary to said secondary data processing system;

said first and second data communications means being connected to said primary and secondary data-storage systems, respectively; and

said primary data-storage system indicating to said primary data processing system that said update data are stored in said first device before said update data are copied to said second device.

10. The apparatus as set forth in claim 9, further including, in combination:

copy session means in said primary data processing system for establishing a data copy session between said primary and secondary data processing systems and being connected to said pending write update means for enabling said pending write update means to establish a sequence of said pending write update sessions within said data copy session; and

said pending write update means having initialization means for establishing each said pending write update session for a predetermined number of update data transfers including generating said sequence numbers for each said pending write update session such that each pending write update session has a unique set of said sequence numbers.

11. A machine-effected method of backing up data stored in first peripheral means of a primary data-storage system of a primary data processing system into second peripheral means of a secondary data-storage system that is physically independent of said first peripheral means;

each said peripheral means in both said data-storage systems having a plurality of first and second device addressable data-storage locations for retentively storing data;

said secondary data-storage system further having primary and secondary temporary data storage having temporary addressable data storage;

primary and secondary directories respectively providing address-ability of data stored in said first and second device;

an update directory in said secondary data-storage system for providing addressability in said temporary data storage and to predetermined data stored in said second peripheral means independently of said secondary directory;

the machine-effected method including machine-executed steps of;

in said primary data processing system establishing a pending write update session in which data in the primary data-storage system are updated by update data that are to be copied from said primary data-storage system to said secondary data-storage system during said pending write update session;

repeatedly updating data in said primary data-storage system including for each said data updates in said primary data processing system, identifying said data updates as being in said established pending write update session including indicating time of updating of each data update;

after updating said primary directory to reflect each said data update for providing addressability to such update data;

sending a copy of each said data update during said pending write update session, including the respective indicated time of updating in said established pending write update session, to said secondary data-storage system;

in said secondary data-storage system responding to receiving said data update and its respective time of updating indication during said pending write update session for storing said data update in said second device and storing said time of updating and an identification of said stored data only in said update directory as respective update directory entries;

in said primary data processing system, indicating to said secondary data-storage system termination of said pending write update session and that said secondary directory is to be updated only with a most recent copy of said update data stored in said second device as indicated by said times of updating, respectively; and

then in said secondary data-storage system updating said secondary directory to indicate said most recent copy of said update data.

12. In the method set forth in claim 11, further including machine-executed steps of:

in said primary data processing system generating and maintaining a current time indication for use in generating said times of updating indications;

in said primary data-storage system, for each of said data updates stored in said first device fetching said current time indication for generating said time of updating indication;

in said secondary data-storage system storing said received time of updating indication with said data updates, respectively, into said secondary temporary data storage;

in said secondary data-storage system, responding to said termination of said pending write update session but before updating said secondary directory, sorting the data updates for every set of plural copies of a same data unit in an order of said time of updating indications for identifying a most recent time of updated copy of each respective same data unit, then using identification of said most recent copy of each said data unit for said secondary directory update.

13. The method set forth in claim 12, further including machine-executed steps of:

in said first device establishing a plurality of first subsystems for connecting all of said addressable first data storage devices to said primary data processing system whereby said first data storage devices and said primary temporary data storage can be accessed by any one of said first subsystems;

generating a predetermined set of sequence numbers and assigning a subset of said sequence numbers to respective first subsystems;

in said primary data-storage system assigning one of said sequence numbers to each of said data updates, respectively, for indicating which of said first subsystems transferred said data updates to said primary temporary data storage;

adding each of said sequence numbers to the respective update data being copied to said secondary data-storage system; and

in said secondary secondary data-storage system, first sorting the update data indications by said data units, then checking completeness of said sequence numbers and then sorting said update data indications by said time of updating indications for finding and selecting said most recent copy of each said data unit.

14. The method set forth in claim 13, further including machine-executed steps of:

establishing in each said secondary data-storage system a log structured array;

in said log structured array providing N ones of said addressable second data storage devices, N being a positive integer;

in said log structured array, dividing said addressable data-storage locations into a plurality of addressable data-storing segments, making each of said plurality of segments to consist of a column segment in each of said second data storage devices, respectively, wherein addresses of said column segments in any of said N ones of said addressable second data storage devices having identical addresses within the respective N ones of said second addressable data storage devices;

in said log structured array providing data compression means for compressing all data stored in said log structured array;

in said secondary data-storage system, updating said log structured array including writing updated data and all non-updated original data in a new addressable area of said log structured array; and

then updating the secondary directory to indicate only said new addressable data.

15. The method set forth in claim 12, further including machine-executed steps of:

in said secondary data-storage system providing a non-volatile random access control memory; and

storing said secondary directory in said non-volatile random access control memory.

16. The method set forth in claim 12, further including machine-executed steps of:

storing said sequence numbers in said primary data-processing system, said time of updating indications and identifications of the data units for each copy of data for the respective data units;

responding to said termination of said pending write update session to supply to said secondary data-processing system an indication of a predetermined range of said stored sequence numbers and said time of updating for each said stored sequence number in said predetermined range; and

in said secondary data-storage system selecting from said update directory all of said update directory entries having ones of said sequence numbers lying within said range of indications for identifying said most recent copies of the respective data units.

17. The method set forth in claim 16, further including machine-executed steps of:

in said step of establishing said pending write update session, assigning a session ID to said session; and

including said session ID with each copy of said update data copied from said primary data-storage system to said secondary data-storage system.

18. A delayed directory updating control apparatus for use with dual mode remote data copy apparatus for transferring updated data between primary and secondary data-storage systems, said primary and secondary data-storage systems having primary and secondary long-term storage comprising first and second peripheral means, respectively, each said peripheral means in both said data-storage systems having a plurality of first and second device addressable data-storage locations for retentively storing data, primary and secondary directories respectively providing addressability of data stored in said first and second peripheral means, said data being arranged in addressable data units that are successively updated by replacing current data with update data in each data unit;

said delayed directory updating control apparatus including, in combination;

pending write update means in said primary data processing system for establishing a pending write update session in which data in the primary data-storage system are updated by update data and are to be copied to said secondary data-storage system wherein said secondary directory is updated after termination of said established pending write update session;

primary data update means in said primary data-storage system and connected to said pending write update means for responding to said pending write update session for repeatedly storing data in said first peripheral means and updating said primary directory to reflect storage of said update data, assigning a time of updating to each update for indicating time that update data are respectively stored in said first peripheral means,

system inter-communication terminal means connected to said primary data-storage system and to said pending write update means and being responsive to said pending write update means established pending write update session and to said primary data update means updating data stored in said first peripheral means for receiving for transmittal to said secondary data-storage system a copy of said update data and said time of updating and indicating that said copy of said update data is transmitted as a part of said pending write update session;

consistency means connected to said secondary data-storage system for indicating termination of said pending write update session and that said secondary directory is to be updated with addresses only for a most recent copy of said transmitted update data; and

said consistency means further indicating to said system inter-connection terminal means to indicate termination of said pending write update session to said secondary data-storage system for immediately updating said secondary directory only with addresses for said most recent updated copies of said update data.

19. A secondary delayed directory updating system for use in a dual remote data copy apparatus for copying updated data from a primary data-storage system to a secondary data-storage system, said primary and secondary data-storage systems having primary and secondary long-term storage comprising first and second peripheral means, respectively,

each said peripheral means in both said data-storage systems having a plurality of first and second device addressable data-storage locations for retentively storing data, primary and secondary directories respectively providing addressability of data stored in said first and second peripheral means;

said delayed directory updating system including, in combination;

an update directory providing addressability of said data copied from said primary data-storage system and stored in said secondary data-storage system;

said secondary directory providing addressability of data stored in said secondary data-storage system that are other than said copied data;

system inter-communication terminal means for being connected to said primary data-storage system for receiving from the primary data-storage system update data to be stored in the secondary data-storage system, time of updating indications with said received data and an indication that the received data are in a predetermined pending write update session;

data update means being connected to said system inter-connection terminal means for receiving said update data, said time of updating indications and said indication of a pending update session for storing said received update data, time of updating indication and said pending write update session indication in said primary data-storage system;

said data update means in said secondary data-storage system connected to said update directory and to said system inter-connection terminal means for responding to receiving said update data in said pending write update session for storing said update data in said secondary data-storage system and to update said update directory;

said system inter-communication terminal means supplying an indication of termination of said pending write update session; and

connected to said secondary directory, said update directory and to said system inter-connection terminal means for being responsive to said termination indication to sort the time of updating indications, order the indications of said received data in the order of said time of updating indications for indicating a most recent copy of each data unit copied into said secondary data-storage system, selection means in the directory update means for updating said secondary directory using addresses of said most recent copy of each data unit to then be included as a part of said other than said copied data.

20. A data-storage system having means for deferred updating of a directory for said data-storage system, including, in combination:

a plurality of addressable data storage locations for retentively storing data;

directory means for indicating which of said addressable data storage locations are storing data and identification of such data;

input means connected to said addressable data storage locations for repeatedly supplying copies of data units to be stored in said addressable data storage locations;

update means in the data input means for storing in respective ones of said addressable data storage locations said supplied copies of said data units at predetermined ones of said addressable data storage locations and being connected to said directory means for indicating addresses of said addressable data storage locations whereat said copies of said data units are stored;

indication means in the input means for supplying a time stamp with each of said supplied copies of said data units such that a plurality of copies of predetermined ones of said data units each with a different time stamp are supplied by said input means;

logging means in said data input means for storing said time stamps and respective identifications of said supplied and stored copies of data units for pointing to said plurality of copies of the respective data units stored in said addressable data storage locations;

end means in said data input means for indicating that said directory is to be updated to address only those copies of said respective data units having a most recent time stamp and not to store any of said copies of said data units having less recent ones of said time stamps, respectively; and

directory update means connected to said end means, to said logging means and to said directory for responding to said indication to sort said time stamps for copies of each said data units for indicating said most recent copy of said data units, respectively, and for updating said directory only with said sorted most recent copy address.

21. In the system set forth in claim 20 further including, in combination:

sequence number means in said data input means for supplying a sequence number for each copy of said supplied data units; and

said directory update means having checking means connected to said sequence number means for checking that said supplied sequence numbers are a continuous sequence without any missing sequence numbers, then actuating said directory update means to update said directory.

22. In the system set forth in claim 20 further including, in combination:

said addressable data storage locations comprising a log structured array having N data-storage devices, said array being divided into a plurality of addressable data-storing segments, each of said plurality of segments consisting of a column segment in each of said data-storage devices, respectively, wherein addresses of said column segments in any of said data-storage devices having identical addresses within the respective data-storage devices.

23. In a machine-effected method of storing data in a data-storage system having a plurality of addressable data storage locations, a directory means for addressing data stored in said plurality of addressable data storage locations, including machine-executed steps of:

repeatedly receiving from a data input means copies of data units to be stored in said addressable data storage locations including plural copies of predetermined ones of said data units and receiving a time stamp with each said copy of said data units, each said time stamp having a predetermined time indication;

storing all of said received copies of said data units in respective ones of said addressable data storage locations;

storing each said time stamp and an identification of said data unit and address of said respective ones of said addressable data storage locations in a logging means;

indicating that a directory is to be updated for indicating addresses of a most recent copy of each of said data units as indicated by the respective time stamps;

in said logging means, responding to said update indicating for sorting said indications of all copies for the respective data units by said respective time stamps for identifying the copies of said data units that have a most recent time indication, respectively for each of said data units as identified most-recent copies; and

storing said addresses of said identified most recent copies of said data units in said directory such that said directory has addresses only for the most-recent copies of said data units and no addresses for any copy of said data units with a time stamp that is other than said most recent time stamp of the respective data units.

24. In the machine-effected method set forth in claim 23, further including machine-executed steps of:

receiving from said data input means a sequence number with each said copy of said data units with said sequence numbers of all said copies being in predetermined sets of continuous sequences of numbers for indicating that all copies of said data units identified by said sequence numbers in said set have been received; and

delaying said sorting of said indications until all said sequence numbers in said set have been received whereby the directory is not updated until all copies indicated by said sequence numbers in said set have been received and stored in said addressable data storage locations.

25. In the machine-effected method set forth in claim 24, further including machine-executed steps of:

providing a log structured array having said addressable data storage locations disposed in N addressable data storage data storage devices, dividing said array into a plurality of data-storing segments, putting a like-predetermined number of said addressable data storage locations in each of said data-storing segments, each of said plurality of segments consisting of a column segment in each of said data storage devices, respectively, wherein addresses of said column segments in any of said devices having identical addresses within the respective data storage devices.

26. A computer program product for backing up data stored in first peripheral means of a primary data-storage system of a primary data processing system into second peripheral means of a secondary data-storage system that is physically independent of said first peripheral means;

each said peripheral means in both said data-storage systems having a plurality of first and second device addressable data-storage locations for retentively storing data;

said secondary data-storage system further having primary and secondary temporary data storage having temporary addressable data storage;

primary and secondary directories respectively providing addressability of data stored in said first and second device;

the computer program product having data storage means containing machine-sensible-and-executable program instructions, which include the following;

program instructions for establishing in said primary data processing system a pending write update session in which data in the primary data-storage system are updated by update data that are to be copied from said primary data-storage system to said secondary data-storage system during said pending write update session;

program instructions responsive to said primary data processing system repeatedly updating data in said primary data-storage system to include during said pending write update session for each one of said data updates in said primary data processing system identifying said data updates as being in said established pending write update session including indicating time of updating of each said data update;

program instructions for establishing an update directory in said secondary data-storage system for providing addressability in said secondary data storage independently of said secondary directory;

program instructions for sending a copy of each said data update during said pending write update session, including the respective indicated time of updating in said established pending write update session, to said secondary data-storage system;

program instructions for responding to receiving said data update and its respective time of updating indication during said pending write update session for storing said data update in said second device and storing said time of updating and an identification of said stored data only in said update directory as respective update directory entries;

program instructions for indicating to said secondary data-storage system termination of said pending write update session and that said secondary directory is to be updated only with a most recent copy of said update data stored in said second device as indicated by said times of updating, respectively; and

program instructions for responding to said indicated end of update session for reading said update directory entries for updating said secondary directory to indicate said most recent copy of said update data.

27. A computer program product for delayed updating a secondary directory for use in a dual remote data copy data processing system for copying updated data from a primary data-storage system to a secondary data-storage system, said primary and secondary data-storage systems having primary and secondary long-term storage comprising first and second peripheral means, respectively, each said peripheral means in both said data-storage systems having a plurality of first and second device addressable data-storage locations for retentively storing data, primary and secondary directories respectively providing addressability of data stored in said first and second peripheral means;

said computer program product having a data storage means storing machine-sensible-and-executable program instructions which include;

program instructions to create an update directory for providing addressability of said data copied from said primary data-storage system and stored in said secondary data-storage system;

program instructions for establishing a system inter-communication terminal program for connecting a secondary data storage system to said primary data-storage system for receiving from the primary data-storage system update data to be stored in the secondary data-storage system, time of updating indications with said received data and an indication that the received data are in a predetermined pending write update session;

program instructions for creating a data update program connected to said system inter-connection terminal program for receiving said update data, said time of updating indications and said indication of a pending update session for storing said received update data, time of updating indication and said pending write update session indication in said primary data-storage system;

program instructions for interconnecting said data update program in said secondary data-storage system to said update directory and to said system inter-connection terminal program for responding to receiving said update data in said pending write update session for storing said update data in said secondary data-storage system and to update said update directory;

program instructions for supplying an indication of termination of said pending write update session;

program instructions responding to said termination indication to read said update directory to sort said time of updating indications, order the indications of said received data in the order of said time of updating indications for indicating a most recent copy of said data units copied into said secondary data-storage system; and

program instructions for updating said secondary directory using addresses of said most recent copy of each said data unit indicated in said update directory to then be included as a part of said other than said copied data.

28. A computer program product for controlling storing data in a data-storage system having a plurality of addressable data storage locations, a directory means for addressing data stored in said plurality of addressable data storage locations;

said computer program product having data storage means containing machine-sensible-and-executable program instructions which include the following;

program instructions for repeatedly receiving from a data input means copies of data units to be stored in said addressable data storage locations including plural copies of predetermined ones of said data units and receiving a time stamp with each said copy of said data units, each said time stamp having a predetermined time indication;

program instructions for storing all of said received copies of said data units in respective ones of said addressable data storage locations;

program instructions for storing each said time stamp and an identification of said data unit and address of said respective ones of said addressable data storage locations in a log;

program instructions for indicating that a directory is to be updated for indicating addresses of a most recent copy of each of said data units as indicated by the respective time stamps;

program instructions for responding to said indicating that said directory is to be updated to access said log for sorting said indications of all copies for the respective data units by said respective time stamps for identifying the copies of said data units that have a most recent time indication, respectively for each of said data units as identified most-recent copies; and

program instructions for storing said addresses of said identified most recent copies of said data units in said directory such that said directory has addresses only for the most-recent copies of said data units and no addresses for any copy of said data units with a time stamp that is other than said most recent time stamp of the respective data units.