Method and apparatus for providing a disc drive snapshot backup while allowing normal drive read, write, and buffering operations

• US 6,182,198 B1
• Filed: 06/04/1999
• Issued: 01/30/2001
• Est. Priority Date: 06/05/1998
• Status: Expired due to Term

• Current Assignee: Xyratex Technology Limited (Seagate Technology Holdings Plc)
• Original Assignee: International Business Machines Corporation
• Inventors: Hubis, Walter A., Otterness, Noel S.
• Primary Examiner(s): Chan, Eddie P.
• Assistant Examiner(s): Kim, Hong
• Application Number:
  US09/326,498
• Time in Patent Office: 606 Days
• Field of Search: 711/162, 711/114, 711/113, 711/112, 714/6, 707/204
• US Class Current: 711/162
• CPC Class Codes: G06F 11/1466 to make the backup process non-disruptive
• CPC Class Codes: G06F 11/1662 the resynchronized component or unit being a persistent storage device re-synchronization of failed mirror storage G06F11/2082; rebuild or reconstruction of parity RAID storage G06F11/1008
• CPC Class Codes: G06F 11/2094 Redundant storage or storage space G06F11/2056 takes precedence
• CPC Class Codes: G06F 2201/84 Using snapshots, i.e. a logical point-in-time copy of the data
• CPC Class Codes: Y10S 707/99953 Recoverability
• CPC Class Codes: Y10S 707/99955 Archiving or backup

Abstract

The present invention is a method and system of performing a snapshot backup of a storage unit of a host system. The host system includes at least one primary system drive, a primary logic unit, a log system drive and at least one backup logic unit. A particular method is designed to perform the snapshot backup while allowing normal read operations and write operations to occur. After initializing the snapshot backup, the method processes a write operation of new data submitted to the primary logic unit to be written to the primary system drive during the snapshot backup by reading the old data that is on the primary system drive, buffering the old data, overwriting the old data and writing the old data to the log system drive if the write operation is the first write operation to a specific sector in the primary system drive for the snapshot backup. The method executes a read operation during the snapshot backup by processing the read operation submitted to the backup logic unit by accessing the requested data from the log system drive if the requested data is available from the log system drive, if not, accessing the requested data from the primary system drive.

Claims

1. A method of performing a snapshot backup of a storage unit of a host system including at least one primary system drive, at least one log system drive and at least one backup logic unit while allowing normal read operations and write operations to occur, comprising:

a) processing a write operation of new data submitted to a primary logic unit to be written to at least one sector of the primary system drive during the snapshot backup including;

i) reading old data on the primary system drive that is to be overwritten by the new data in response to the write operation;

ii) buffering the old data;

iii) overwriting the old data with the new data; and

iv) writing the old data to the log system drive if the write operation is a first write operation to the sector in the primary system drive for the snapshot backup;

(b) processing a read operation submitted to the backup logic unit during the snapshot backup including;

i) accessing requested data of the read operation from the log system drive if the requested data is available from the log system drive and returning the requested data;

ii) accessing the requested data from the primary system drive if the requested data is not available from the log system drive and returning the requested data.

2. The method of performing a snapshot backup of claim 1, further comprising the step of:

flushing any data from an internal cache of the host system.

3. The method of performing a snapshot backup of claim 1, further comprising the step of:

writing the old data to the log system drive after the overwriting of the old data with the new data has completed.

4. The method of performing a snapshot backup of claim 1 wherein:

responding with an error code from the backup logic unit when the log drive becomes full and entering the backup logic unit into a drive not ready state.

5. The method of performing a snapshot backup of claim 1 wherein:

accessing the backup logic unit from at least two controllers.

6. The method of performing a snapshot backup of claim 5 wherein:

at least one of the two controllers is a RAID controller.

7. The method of performing a snapshot backup of claim 1 further comprising:

preserving the snapshot backup through a second controller in the event a failure of a first controller occurs.

8. The method of performing a snapshot backup of claim 1 wherein:

notifying a second controller through back-end SCSI channels when a first controller initiates a snapshot backup;

initializing information regarding the log system drive by the second controller; and

monitoring a normal write cache mirroring to maintain ongoing changes to the log system drive during the snapshot backup.

9. The method of performing a snapshot backup of claim 1 wherein:

accessing the backup logic unit from at least one controller that is different than a controller accessing the primary logic unit.

10. The method of performing a snapshot backup of claim 1 wherein:

structuring the primary system drive utilizing a RAID strategy.

11. The method of performing a snapshot backup of claim 1 wherein:

utilizing the log system drive with more than one primary system drive and limiting the snapshot backup to a single primary system drive at any given time.

12. The method of performing a snapshot backup of claim 1 wherein:

directing No an initializing of the snapshot backup to the primary logic unit coupled to the primary system drive.

13. The method of performing a snapshot backup of claim 1 wherein:

directing a terminating of the snapshot backup to one of the primary logic unit coupled to the primary system drive and the backup logic unit.

14. A method of performing a snapshot backup of a storage unit of a host system including at least one controller, at least one primary system drive, a log system drive, at least one logic unit and a buffer while allowing normal read operations and write operations to occur comprising:

a) initializing the snapshot backup;

b) issuing a system drive copy command to the controller and copying the log system drive to at least one backup system drive;

c) processing a read operation submitted to the logic unit coupled to the log system drive during the snapshot backup including;

i) accessing requested data of the read operation from the log system drive if the requested data is available from the log system drive and returning the requested data to a requester;

ii) accessing the requested data from the primary system drive if the requested data is not available from the log system drive and returning the requested data to the requester;

d) processing a write operation of new data submitted to a primary logic unit to be written to a sector of the primary system drive during the snapshot backup including;

i) reading old data on the primary system drive that is to be overwritten by the new data in response to the write operation;

ii) buffering the old data in the buffer;

iii) overwriting the old data with the new data;

iv) writing the old data from the buffer to the log system drive if the write operation is a first write operation to the sector in the primary system drive for the snapshot backup; and

e) terminating the snapshot backup.

15. The method of performing a snapshot backup of claim 14 wherein:

designating the logic unit coupled to the backup drive system as a backup logic unit and responding with a busy status to the read operation or the write operation issued to the backup logic unit while the copying of the log system drive to the backup system drive is in progress.

16. The method of performing a snapshot backup of claim 14 wherein:

the backup system drive is at least equal in size to the primary system drive.

17. The method of performing a snapshot backup of claim 14 wherein:

configuring the log system drive and the backup system drive onto the same controller.

18. The method of performing a snapshot backup of claim 17 further comprising:

monitoring the copying of the log system drive to the backup system drive through a system drive copy status command.

19. The method of performing a snapshot backup of claim 14 further comprising:

monitoring changes to the sectors of the primary system drive following the termination of the snapshot backup and copying only those sectors that have changed since the termination of the snapshot into the backup system drive.

20. A storage unit of a host system including at least one primary system drive, at least one log system drive and at least one backup logical unit adapted to create a snapshot backup comprising:

a) means for initializing a snapshot backup coupled with a means for processing a read operation, and further coupled with a means for processing a write operation;

b) the means for processing the read operation submitted to a backup logic unit during the snapshot backup including;

i) means for accessing requested data of the read operation from the log system drive if the requested data is available from the log system drive and returning the requested data;

ii) means for accessing the requested data from the primary system drive if the requested data is not available from the log system drive and returning the requested data; and

c) the means for processing a write operation of new data submitted to a primary logic unit to be written to at least one sector of the primary system drive during the snapshot backup including;

i) means for reading old data on the primary system drive that is to be overwritten by the new data in response to the write operation;

ii) means for buffering the old data;

iii) means for overwriting the old data with the new data; and

iv) means for writing the old data to the log system drive if the write operation is a first write operation to the sector in the primary system drive for the snapshot backup.

21. The storage unit of a host system adapted to create a snapshot backup as claimed in claim 20, wherein:

the means for processing the read operation comprising at least a controller; and

the means for processing the write operation comprising at least the controller.

22. A storage unit of a host system adapted to create a snapshot backup, comprising:

a) at least one controller which initializes and terminates the snapshot backup;

b) at least one backup logic unit electronically coupled to a log system drive such that requested data is accessed from the log system drive if the requested data is available from the log system drive during a read operation and returned to a requester;

c) the backup logic unit electronically coupled to at least one primary system drive such that the requested data is accessed from the primary system drive if the requested data is not available from the log system drive during the read operation and returned to the requester;

d) at least one primary logic unit electronically coupled to the primary system drive such that new data submitted to the primary logic unit is written to a sector of the primary system drive;

e) a buffer electronically coupled to the primary system drive such that old data that is to be overwritten by the new data submitted to the primary logic unit is buffered prior to being overwritten;

f) the buffer further electronically coupled to the log system drive such that the old data is written to the log system drive if the new data written to the primary system drive is the first data to be written to the sector during the snapshot backup; and

g) a backup system drive electronically coupled with the log system drive, and configured to store a copy of at least a portion of data stored within the log system drive.

23. A computer program product for performing a snapshot backup of a storage unit of a host system including at least one primary system drive, at least one log system drive and at least one backup logic unit while allowing normal read operations and write operations to occur, the computer program product including a computer readable medium and a computer program mechanism stored thereon, the computer program mechanism comprising:

a snapshot backup procedure configured to;

process a read operation submitted to the backup logic unit during the snapshot backup, including;

accessing requested data of the read operation from the log system drive if the requested data is available from the log system drive and returning the requested data;

accessing the requested data from the primary system drive if the requested data is not available from the log system drive and returning the requested data;

process a write operation of new data submitted to a primary logic unit to be written to the primary system drive during the snapshot backup including;

reading old data on the primary system drive that is to be overwritten by the new data in response to the write operation;

buffering the old data;

overwriting the old data with the new data; and

writing the old data to the log system drive if the write operation is a first write operation to a sector in the primary system drive for the snapshot backup.

24. A computer program product for performing a snapshot backup of a storage unit of a host system including at least one controller, at least one primary system drive, a log system drive, at least one logic unit and a buffer while allowing normal read operations and write operations to occur, the computer program product including a computer readable medium and a computer program mechanism stored thereon, the computer program mechanism comprising:

a snapshot backup process configured to;

copy the log system drive to at least one backup system drive;

process a read operation submitted to the logic unit coupled to the log system drive during the snapshot backup including;

accessing requested data of the read operation from the log system drive if the requested data is available from the log system drive and returning the requested data;

accessing the requested data from the primary system drive if the requested data is not available from the log system drive and returning the requested data;

process a write operation of new data submitted to a primary logic unit to be written to at least one sector of the primary system drive during the snapshot backup including;

reading old data on the primary system drive that is to be overwritten by the new data in response to the write operation;

buffering the old data in the buffer;

overwriting the old data with the new data; and

writing the old data from the buffer to the log system drive if the write operation is a first write operation to the sector in the primary system drive for the snapshot backup.

25. A snapshot backup system for use by a host computer, comprising:

least one primary system drive where data is written and read during normal operation of the backup system;

one or more primary logical units through which the primary system drive is accessed by the host, each of the primary logical units including a physical interface and a logical interface;

at least one log system drive where data is written for backup purposes during backup operation of the backup system;

one or more backup logical units through which the log system drive is accessed by the host, each of the backup logical units including a physical interface and a logical interface;

wherein, during the backup operation;

the snapshot backup system is configured to respond to write requests targeting the primary system drive by;

reading and buffering the data in at least one sector of the primary system drive that is to be overwritten by a write request;

when the write request is the first request to write to the sector, writing the data to the log system drive; and

completing the write request to the primary system drive; and

the snapshot backup system is configured to respond to read requests targeting the log system drive by;

returning the data fulfilling a read request from the log system drive when possible; and

otherwise returning the data to fulfill the read request from the primary system drive.

26. A method of performing a snapshot backup of a storage unit of a host system including at least one primary system drive, at least one log system drive, at least one backup system drive, and at least one logic unit while allowing normal read operations and write operations to occur comprising:

a) copying the log system drive to the backup system drive;

b) processing a read operation submitted to the logic unit during the snapshot backup including;

i) accessing requested data of the read operation from the log system drive if the requested data is available from the log system drive and returning the requested data;

ii) accessing the requested data from the primary system drive if the requested data is not available from the log system drive and returning the requested data; and

c) processing a write operation of new data submitted to a primary logic unit to be written to at least one sector of the primary system drive during the snapshot backup including;

i) reading old data on the primary system drive that is to be overwritten by the new data in response to the write operation;

ii) buffering the old data;

iii) overwriting the old data with the new data; and

iv) writing the old data to the log system drive if the write operation is a first write operation to the sector in the primary system drive for the snapshot backup.

27. The method of performing a snapshot backup as claimed in claim 26, wherein:

preserving the snapshot backup through a second controller in the event a failure of a first controller occurs.