Apparatus and method of null data skip remote copy

• US 20040088505A1
• Filed: 10/31/2002
• Published: 05/06/2004
• Est. Priority Date: 10/31/2002
• Status: Active Grant

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Watanabe, Naoki
• Granted Patent: US 7,024,526 B2
• Time in Patent Office: Days
• US Class Current: 711/161
• CPC Class Codes: G06F 11/2071 using a plurality of controllers
• CPC Class Codes: G06F 11/2082 Data synchronisation
• CPC Class Codes: G06F 3/0608 Saving storage space on storage systems
• CPC Class Codes: G06F 3/0613 in relation to throughput
• CPC Class Codes: G06F 3/065 Replication mechanisms
• CPC Class Codes: G06F 3/067 Distributed or networked storage systems, e.g. storage area networks [SAN], network attached storage [NAS]
• CPC Class Codes: Y10S 707/99953 Recoverability
• CPC Class Codes: Y10S 707/99955 Archiving or backup

Abstract

A method and apparatus are provided for enhancing the performance of storage systems is described. In the making of an initial copy to a secondary subsystem, or in the initial storage of data onto a primary storage subsystem, null data is skipped. The data may be skipped by sending the non-null data in sequence so missing addresses are identified as being null data, or a skip message may be used to designate regions where null data is to be present.

Claims

1. A method for copying information from a primary storage system to a secondary storage system, the method comprising:

at the primary storage system, analyzing the information to be copied to determine if it constitutes data desired to be copied or null data which does not need to be copied;

transmitting to the secondary storage system the data desired to be copied and not transmitting the null data;

at the secondary storage system, writing to a storage unit in the secondary storage system the information to be copied.

2. A method as in claim 1 wherein before the step of at the secondary storage system copying to a storage unit, a step is performed of formatting the storage unit to contain null data.

3. A method as in claim 1 further including the step of transmitting to the secondary storage system a skip message which indicates that a block of null data is present on the primary storage system and will not be transmitted to the secondary storage system.

4. A method as in claim 3 wherein after receiving the skip message the secondary storage system writes null data onto the storage unit.

5. A method as in claim 1 wherein the step of transmitting further comprises transmitting to the secondary storage system a pattern of null data to be written onto the secondary storage system at the location where null data would have been stored had it been transmitted to the secondary storage system.

6. A method as in claim 3 wherein the skip message further comprises a pattern for data to be written onto the secondary storage system at the location where null data would have been stored had it been transmitted to the secondary storage system.

7. A method as in claim 1 wherein the primary storage system includes a disk controller and the disk controller performs the step of analyzing the information to be copied to determine if it constitutes data desired to be copied or null data.

8. A method as in claim 1 wherein:

the data to be copied is transmitted from the primary storage system to the secondary storage system in a sequential order; and

the secondary storage system writes null data onto the storage unit when the secondary storage unit detects gaps in the sequential order.

9. A method as in claim 1 wherein the step of analyzing the information is performed as the information is transmitted on a bus in the primary storage system.

10. A method as in claim 9 wherein a DMA controller is used to snoop the bus and analyze the information.

11. In a system having a host and a storage system coupled to the host, the storage system including a channel controller coupled to the host and apparatus for storing data, a method for writing data into the apparatus comprising:

monitoring the data as it is transferred to the storage system;

when a block of data consists only of null data sending a skip message to the apparatus to cause the apparatus not to write that null data; and

when a block of data consists of non-null data sending that data to the apparatus and causing the apparatus to write that data.

12. A method as in claim 11 wherein before the non-null data is written, a step is performed of formatting the apparatus to contain null data.

13. A method as in claim 11 wherein the skip message indicates the address of the null data.

14. A method as in claim 13 wherein the skip message also indicates an amount of null data.

15. A method as in claim 13 wherein after receiving the skip message the apparatus writes null data at the address of the null data.

16. A method as in claim 11 wherein the skip message further comprises a pattern for the null data and the address of the null data.

17. A method as in claim 16 wherein after receiving the skip message the apparatus writes the pattern for the null data at the address of the null data.

18. A method as in claim 11 wherein the storage subsystem includes a disk controller and the disk controller performs the step of analyzing the information to be copied to determine if it constitutes null data.

19. In a storage system operating under computer control and coupled to receive information to be stored as well as specified addresses at which the information is to be stored, the information including null data and non-null data, a method comprising:

monitoring the specified addresses to determine if there are any missing addresses in the addresses received; and

writing null data at the missing addresses.

20. A method as in claim 19 further comprising writing the non-null data at the specified addresses.

21. At a primary storage system, a method of selecting stored data to send from the primary storage system to a secondary storage system comprising:

reading a selected amount of the stored data;

determining if the stored data is null data or non-null;

if the stored data is non-null data then sending it with a command to the secondary storage system to cause the secondary storage system to store the data;

if the stored data is null data then not sending it to the secondary storage system; and

repeating the preceding steps until all of the stored data has been either sent to the secondary system or has been determined to be null data.

22. A method as in claim 21 wherein the step of if the stored data is null data then not sending it to the secondary storage system further comprises sending to the secondary storage system a message indicating that null data has not been sent.

23. A method as in claim 22 wherein the message indicates an address of the null data and a quantity of the null data.

24. At a secondary storage system coupled to receive data transmitted from a primary storage system, a method of storing data transmitted from the primary system comprising:

receiving a command from the primary storage system to store data that will be transmitted from the primary storage system;

receiving the transmitted data from the primary storage system;

receiving a series of addresses, each for a selected amount of the transmitted data;

analyzing the series of addresses to determine if addresses have been skipped in a sequence of addresses;

storing the data at locations specified by the addresses;

storing null data at addresses that have been skipped in the series of addresses;

repeating the preceding steps until all of the data transmitted has been stored.

25. A method as in claim 24 wherein the step of storing null data at addresses that have been skipped in the series of addresses is performed by formatting the secondary storage system before the step of storing the data at locations specified by the addresses.

26. A method as in claim 24 wherein the step of storing null data at addresses that have been skipped in the series of addresses is performed by writing a selected data pattern at addresses that have been skipped in the series of addresses.