METHOD AND APPARATUS FOR SEPARATING SNAPSHOT PRESERVED AND WRITE DATA

• US 20080256141A1
• Filed: 07/19/2007
• Published: 10/16/2008
• Est. Priority Date: 04/11/2007
• Status: Active Grant

• Current Assignee: Dot Hill Systems Corporation (Seagate Technology Holdings Plc)
• Original Assignee: Dot Hill Systems Corporation (Seagate Technology Holdings Plc)
• Inventors: Lee, Kent, Wayda, James George, Rodriguez, Elizabeth G., Vu, Ngoclan Thi
• Granted Patent: US 7,975,115 B2
• Time in Patent Office: Days
• US Class Current: 707/203
• CPC Class Codes: G06F 11/1446 Point-in-time backing up or restoration of persistent data
• CPC Class Codes: G06F 11/2007 using redundant communication media
• CPC Class Codes: G06F 11/2089 Redundant storage control functionality
• CPC Class Codes: G06F 2201/84 Using snapshots, i.e. a logical point-in-time copy of the data
• CPC Class Codes: G06F 3/0608 Saving storage space on storage systems
• CPC Class Codes: G06F 3/0644 Management of space entities, e.g. partitions, extents, pools
• 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]

Abstract

A method and device for managing snapshot data is provided. Snapshots may be created having a preserved data area and a write data area. The preserved data area is used to maintain snapshot data corresponding to the point-in-time when the snapshot was created while the write data area is used to facilitate host read/write access to the snapshot. By maintaining two separate areas, the snapshot can be written to without altering the point-in-time representation of the snapshot.

Claims

1. A method of managing snapshot data, comprising:

at a first point-in-time, receiving a command to create a snapshot;

allocating a first set of memory addresses for storage of preserved data in association with the snapshot; and

allocating a second set of memory addresses for storage of write data in association with the snapshot, wherein the second set of memory addresses are host writeable.

2. The method of claim 1, wherein the first set of memory addresses are alterable by a copy on write operation.

3. The method of claim 1, further comprising:

receiving a command to write data to the snapshot;

determining whether the command is controller initiated or host initiated;

in the event that the write command is controller initiated, writing data to a block range in the first set of memory addresses; and

in the event that the write command is host initiated, writing data to a block range in the second set of memory addresses.

4. The method of claim 1, further comprising:

receiving a first command from a host to modify the snapshot; and

modifying the snapshot according to the first command received from the host.

5. The method of claim 4, further comprising:

receiving a second command to restore the snapshot to the first point-in-time; and

deleting data stored in the second set of memory addresses.

6. The method of claim 4, further comprising:

receiving a second command to read data from the snapshot corresponding to the first point-in-time; and

reading data from the first set of memory addresses.

7. The method of claim 1, wherein a first block range in the first set of memory addresses corresponds to a first block range in the second set of memory addresses and wherein data stored in the first block range of the first set of memory addresses corresponds to the first point-in-time and wherein data stored in the first block range of the second set of memory addresses corresponds to a second point-in-time that is later than the first point-in-time.

8. The method of claim 1, wherein at least one of the first and second sets of memory addresses are dynamically allocated.

9. The method of claim 1, further comprising:

receiving a command to read data from the snapshot;

in response to receiving the command to read data, searching the second set of memory addresses to determine if the requested data resides therein; and

in the event that the requested data does not reside in the second set of memory addresses, searching the first set of memory addresses to determine if the requested data resides therein.

10. A device for managing snapshot data, comprising:

an input operable to receive instructions to create a snapshot of a master volume at a first point-in-time; and

a snapshot application operable to create a first snapshot in response to receiving the instructions, wherein the first snapshot comprises two separate data storage areas for storing different instances of data corresponding to a common data block range on the master volume, wherein a first of the two data storage areas is used to store preserved data and wherein a second of the two data storage areas is used to store write data.

11. The device of claim 10, wherein the preserved data is alterable by a copy on write operation and the write data is alterable by a host.

12. The device of claim 10, wherein the preserved data substantially corresponds to the first point-in-time and the write data corresponds to a second point-in-time after the first point-in-time.

13. The device of claim 10, wherein upon receiving instructions to modify the snapshot at the input, the snapshot application is further operable to modify the snapshot according to the modify command received at the input.

14. The device of claim 13, wherein after receiving the modify command and upon receiving instructions to restore the snapshot to the first point-in-time at the input, the snapshot application is further operable to delete data from the second of the two data storage areas.

15. The device of claim 10, further comprising and I/O application, wherein after receiving a read command, the I/O application is operable to search the second of the two data storage areas to determine if the requested data resides therein and in the event that the requested data does not reside in the second of the two data storage areas, search the first of the two data storage areas to determine if the requested data resides therein.

16. The device of claim 15, wherein in the event that the requested data does not reside in either of the two data storage areas, the I/O application is further operable to search preserved data areas of snapshots that were created after the first point-in-time.

17. A data storage device, comprising:

a snapshot having two separate data storage areas for storing different instances of data corresponding to a common data block range on a master volume, wherein a first of the two data storage areas is used to store preserved data and wherein a second of the two data storage areas is used to store write data.

18. The device of claim 17, wherein the preserved data and write data are accessible independent of one another.

19. The device of claim 17, wherein the preserved data is alterable by a copy on write operation and the write data is alterable by a host.

20. The device of claim 17, wherein the preserved data substantially corresponds to the first point-in-time and the write data is operable to be modified at any point after the first point-in-time.