METHOD AND APPARATUS FOR QUICKLY ACCESSING BACKING STORE METADATA

• US 20080177954A1
• Filed: 01/18/2007
• Published: 07/24/2008
• Est. Priority Date: 01/18/2007
• 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
• Granted Patent: US 8,751,467 B2
• Time in Patent Office: Days
• US Class Current: 711/154
• CPC Class Codes: G06F 11/1666 where the redundant component is memory or memory area
• CPC Class Codes: G06F 11/2056 by mirroring
• CPC Class Codes: G06F 11/2089 Redundant storage control functionality
• CPC Class Codes: G06F 12/0804 with main memory updating G06F12/0806 takes precedence
• CPC Class Codes: G06F 12/0866 for peripheral storage systems, e.g. disk cache
• CPC Class Codes: G06F 12/126 with special data handling, e.g. priority of data or instructions, handling errors or pinning
• CPC Class Codes: G06F 2212/466 Metadata, control data

Abstract

A method, device, and system are provided for accessing metadata in a data storage system. More specifically, a requesting application requests a cache application to allocate a cache page to retrieve metadata from a storage device. After metadata is written to the cache page, the cache page is locked by the requesting application. The cache page is maintained in a locked state by the requesting application. This allows the data stored within the cache page to be quickly accessed and updated by the requesting application without waiting for the cache page to be written back to the storage device after every update to the cache page occurs.

Claims

1. A method of accessing metadata from a storage device, comprising:

a first application requesting metadata;

a cache application retrieving the requested metadata from a storage device;

writing the metadata from the storage device to an allocated cache page;

the first application assuming control of the cache page with the metadata written thereon;

the first application locking the cache page, wherein locking comprises restricting access to the cache page; and

the first application accessing the metadata from the locked cache page.

2. The method of claim 1, further comprising:

the first application updating the metadata;

the first application writing the updated metadata to the locked cache page; and

mirroring the locked cache page with updated metadata to a remote system.

3. The method of claim 2, further comprising the first application executing a second command during at least one of the writing and mirroring step, wherein the second command includes accessing the metadata from the locked cache page.

4. The method of claim 2, wherein the remote system comprises a second controller and wherein the mirroring step comprises copying the updated metadata from a first controller associated with the first application to a portion of memory on the second controller.

5. The method of claim 1, further comprising:

waiting for a shutdown event to occur;

in response to a shutdown event occurring, the first application unlocking the cache page; and

the cache application writing the metadata on the cache page back to the storage device.

6. The method of claim 5, wherein the cache page is not unlocked and the metadata on the cache page is not written back to the storage device unless the shutdown event occurs.

7. The method of claim 1, wherein the metadata comprises backing store metadata.

8. A device for controlling a storage system, comprising:

a cache memory comprising a cache page;

a cache application for controlling the cache memory; and

a first application operable to request that the cache application allocate the cache page from the cache memory to store metadata, the first application comprising;

a locking function operable to lock the cache page after the metadata has been written to the cache page; and

a metadata reader/writer operable to access the metadata while it is locked by the locking function.

9. The device of claim 8, wherein the locking function maintains the cache page in a locked state until the occurrence of a shutdown event, and wherein the cache page is inaccessible to the cache application while in a locked state.

10. The device of claim 9, wherein a shutdown event comprises an event that causes the power supplied to the cache memory to be interrupted.

11. The device of claim 9, wherein the locking function unlocks the cache page upon detection of the shutdown event thereby allowing the cache application to write the metadata on the cache page back to the storage device.

12. The device of claim 8, wherein the metadata reader/writer changes the metadata and commits the changes to the cache page as a part of accessing the metadata.

13. The device of claim 12, wherein the metadata reader/writer is further operable to execute a second command requiring access to the metadata while the changes to the cache page are being committed.

14. The device of claim 12, wherein the metadata reader/writer mirrors the changes to the cache page to a remote system in the course of committing the changes to the cache page.

15. The device of claim 8, wherein the cache page is maintained in a locked state on at least one of a battery backed volatile memory and capacitor backed volatile memory.

16. An electronic data system, comprising:

first controlling means comprising;

means for reading metadata from a storage device;

means for storing the metadata on a cache page;

means for locking the cache page;

means for accessing the locked cache page; and

means for updating the metadata in the locked cache page, wherein the means for accessing is operable to at least one of commit changes to the locked cache page and mirror changes to a second controlling means while simultaneously accessing the locked cache page.

17. The system of claim 16, wherein the metadata comprises pointers to snapshot data stored on a storage device.

18. The system of claim 16, wherein the metadata is read from the storage device in a first state and changed to a second different state by the means for updating.

19. The system of claim 18, wherein the metadata in the second state is accessed by the means for accessing prior to being written back to the storage device.

20. The system of claim 18, wherein the metadata is further updated to a third state by the means for updating prior to being written back to the storage device.