Granted Patent B1

US 7,647,449 · App. 11/540,822 · Granted Jan 12, 2010

Abstract

Claims (51)

1. A method for maintaining the order of write-commands issued to a data storage, wherein the write-commands are issued by at least one host, the method comprising:

assigning an order-descriptor to each write-command;

storing the write-command;

storing the order-descriptor; and

collating a plurality of order-descriptors and their corresponding write-commands to obtain an ordered write-command stream;

wherein assigning the order-descriptor to the write-command comprises:

assigning an indicia of order to the write-command; and

constructing the order-descriptor using the indicia of order and metadata information for the write-command.

2. The method of claim 1 , wherein constructing the order-descriptor comprises:

receiving the write-command from the host; and

extracting the metadata information from the write-command; and

placing at least some of the metadata information into the order-descriptor.

3. The method of claim 1 , wherein constructing the order-descriptor comprises:

receiving the metadata information from the host.

4. The method of claim 1 further comprising sending an acknowledgement message to the host.

5. The method of claim 1 further comprising updating a backup of the data storage using the ordered write-command stream.

6. The method of claim 1 further comprising rolling back the state of the data storage using the ordered write-command stream.

7. The method of claim 1 , wherein the indicia of order comprises a time-stamp.

8. The method of claim 1 , wherein the indicia of order comprises a monotonically increasing number.

9. The method of claim 1 , wherein the metadata information comprises at least one of:

an initiator of the write-command;

a target volume of the write-command;

a start-offset of the write-command;

a length of the write-command; and

location of the write-command in the data log.

10. A system for maintaining the order of write-commands issued to a data storage, wherein the write-commands are issued by at least one host, the system comprising:

a write-order manager to assign an order-descriptor to each write-command;

a data log associated with the issuing host to store the write-command;

a descriptor log associated to write-order manager to store the order-descriptor; and

a collating module to collate a plurality of order-descriptors from the descriptor log and their corresponding write-commands from the respective data logs to obtain an ordered write-command stream;

wherein the write-order manager comprises:

an ordering logic to assign an indicia of order to the write-command; and

a descriptor generation logic to construct the order-descriptor using the indicia of order and a metadata information for the write-command.

11. The system of claim 10 , wherein the descriptor generation logic comprises a metadata extractor to extract the metadata information of the write-command.

12. The system of claim 10 , wherein the write-order manager comprises an acknowledgement logic to send an acknowledgement message to the host.

13. The system of claim 10 further comprising a backup system to store the ordered write-command stream.

14. A computer readable medium comprising a program that, when executed by a processor, performs a method for maintaining the order of write-commands issued to a data storage, wherein the write-commands are issued by at least one host, the method comprising:

assigning an order-descriptor to each write-command;

storing the write-command;

storing the order-descriptor; and

collating a plurality of order-descriptors and their corresponding write-commands to obtain an ordered write-command stream;

wherein assigning the order-descriptor to a write-command comprises:

assigning an indicia of order to the write-command; and

constructing the order-descriptor using the indicia of order and metadata information for the write-command.

15. The computer readable medium of claim 14 , wherein constructing the order-descriptor comprises:

receiving the write-command from the host; and

extracting the metadata information from the write-command; and

placing at least some of the metadata information into the order descriptor.

16. The computer readable medium of claim 14 , wherein constructing the order-descriptor comprises:

receiving the metadata information from the host.

17. The computer readable medium of claim 14 further comprising updating a backup of the data storage using the ordered write-command stream.

Assignments (17)