System for Maintaining Dirty Cache Coherency Across Reboot of a Node

• US 20150019822A1
• Filed: 08/15/2013
• Published: 01/15/2015
• Est. Priority Date: 07/11/2013
• Status: Abandoned Application

• Current Assignee: Avago Technologies General IP PTE Limited (Broadcom, Inc.)
• Original Assignee: LSI Corporation (Broadcom, Inc.)
• Inventors: Samanta, Sumanesh, Biswas, Sujan, Sheik, Karimulla, Skariah, Thanu Anna, Goli, Mohana Rao
• Application Number:
  US13/967,387
• Publication Number:
  US 20150019822A1
• Time in Patent Office: Days
• US Class Current: 711/135
• CPC Class Codes: G06F 11/00 Error detection; Error correction; Monitoring error detection, correction or monitoring in information storage based on relative movement between record carrier and transducer G11B20/18; monitoring, i.e. supervising the progress of recording or reproducing G11B27/36; in static stores G11C29/00
• CPC Class Codes: G06F 11/1658 Data re-synchronization of a redundant component, or initial sync of replacement, additional or spare unit
• CPC Class Codes: G06F 11/1666 where the redundant component is memory or memory area
• CPC Class Codes: G06F 11/20 using active fault-masking, e.g. by switching out faulty elements or by switching in spare elements
• CPC Class Codes: G06F 11/2092 Techniques of failing over between control units
• CPC Class Codes: G06F 12/0804 with main memory updating G06F12/0806 takes precedence
• CPC Class Codes: G06F 12/0868 Data transfer between cache memory and other subsystems, e.g. storage devices or host systems
• CPC Class Codes: G06F 2212/286 Mirrored cache memory

Abstract

Nodes in a data storage system having redundant write caches identify when one node fails. A remaining active node stops caching new write operations, and begins flushing cached dirty data. Metadata pertaining to each piece of data flushed from the cache is recorded. Metadata pertaining to new write operations are also recorded a corresponding data flushed immediately when the new write operation involves data in the dirty data cache. When the failed node is restored, the restored node removes all data identified by the metadata from a write cache. Removing such data synchronizes the write cache with all remaining nodes without costly copying operations.

Claims

1. A data storage system comprising:

a first node comprising a dirty data cache;

a second node comprising a dirty data cache; and

a data storage element in data communication with the first node and the second node,

wherein;

the first node and the second node are configured to redundantly cache data from one or more write operations;

the second node is configured to;

identify a failure of the first node;

stop caching new write operations;

begin flushing all new write operations to the data storage element;

determine if a new write operation renders dirty data in the second node dirty data cache obsolete;

record metadata pertaining to obsolete dirty data;

identify that the first node is restored; and

send the metadata to the first node; and

the first node is configured to;

receive metadata from the second node; and

remove data identified by the metadata from the first node dirty data cache.

2. The data storage system of claim 1, wherein the second node is further configured to:

begin flushing dirty data from the second node dirty data cache to the data storage element; and

record metadata pertaining to dirty data flushed from the second node dirty

data cache to the data storage element.

3. The data storage system of claim 1, wherein the data storage element is a redundant array of independent disks.

4. The data storage system of claim 1, wherein the data storage element is a direct-attached storage device.

5. The data storage system of claim 1, wherein the data storage element is owned by the first node.

6. The data storage system of claim 5, wherein the second node is further configured to assume ownership of the data storage element.

7. The data storage system of claim 1, wherein:

the data storage element comprises two or more physical disks;

the first node is configured to own at least one physical disk of the two or more physical disks; and

the second node is configured to own at least one physical disk of the two or more physical disks.

8. The data storage system of claim 1, wherein:

the data storage element comprises two or more virtual disks;

the first node is configured to own at least one virtual disk of the two or more virtual disks; and

the second node is configured to own at least one virtual disk of the two or more virtual disks.

9. A node in a data storage system comprising:

a controller;

memory connected to the controller, at least partially configured as a dirty data cache; and

computer executable program code configured to execute on the controller,

wherein the computer executable program code is configured to;

identify a failure of a redundant controller;

stop caching new write operations;

flush all new write operations to a data storage element;

determine if a new write operation renders dirty data in the dirty data cache obsolete;

record metadata pertaining to obsolete dirty data;

identify that the redundant controller is restored; and

send the metadata to the redundant controller.

10. The node of claim 9, wherein the computer executable program code is further configured to:

flush dirty data from the dirty data cache to a data storage element; and

record metadata pertaining to dirty data flushed from the dirty data cache to the data storage element.

11. The node of claim 9, wherein the memory comprises a persistent memory element configured to retain data during a power lose.

12. The node of claim 11, wherein the memory comprises a solid state drive.

13. The node of claim 9, further comprising:

a second controller; and

a second memory connected to the second controller, at least partially configured as a dirty data cache,

wherein the second controller is configured to maintain a dirty data cache identical to the controller.

14. The node of claim 13, wherein identifying the failure of the redundant controller comprises identifying the failure of the second controller.

15. A method for synchronizing multiple write caches comprising:

identifying a failure of a redundant node;

stopping caching new write operations;

flushing all new write operations to a data storage element;

determining if a new write operation renders dirty data obsolete;

recording metadata pertaining to obsolete dirty data;

identifying that the redundant node is restored; and

sending the metadata to the redundant node.

16. The method of claim 15, further comprising:

flushing dirty data from a dirty data cache to a data storage element; and

recording metadata pertaining to dirty data flushed from the dirty data cache to the data storage element.

17. The method of claim 15, further comprising:

receiving the metadata; and

removing data identified by the metadata from a dirty cache in the redundant node.

18. The method of claim 17, further comprising resuming caching write operations.

19. The method of claim 15, further comprising assuming ownership of at least one virtual disk, wherein the at least one virtual disk was previously owned by the failed redundant node.

20. The method of claim 15, further comprising assuming ownership of at least one physical disk, wherein the at least one physical disk was previously owned by the failed redundant node.