Write-back disk cache management

• US 20030120869A1
• Filed: 12/09/2002
• Published: 06/26/2003
• Est. Priority Date: 12/26/2001
• Status: Abandoned Application

• Current Assignee: BOON Storage Technologies Incorporated
• Original Assignee: BOON Storage Technologies Incorporated
• Inventors: Yeo, Boon-Lock, Lee, Edward K.
• Application Number:
  US10/314,142
• Publication Number:
  US 20030120869A1
• Time in Patent Office: Days
• US Class Current: 711/135
• CPC Class Codes: G06F 11/1084 Degraded mode, e.g. caused by single or multiple storage removals or disk failures
• CPC Class Codes: G06F 11/1092 Rebuilding, e.g. when physically replacing a failing disk
• CPC Class Codes: G06F 2211/1038 LFS, i.e. Log Structured File System used in RAID systems with parity
• CPC Class Codes: G06F 2211/1059 Parity-single bit-RAID5, i.e. RAID 5 implementations

Abstract

A method for efficiently utilizing write-back caches in disk drives to build inexpensive, high-performance, reliable disk arrays. In particular, we describe a method for preserving the ordering of writes issued to a disk array consisting of disks that support write-back caching, without requiring the frequent flushing of the write-back cache.

Claims

1. A method of storing data that preserves an order of writes on a disk storage subsystem with write-back cache turned on comprising:

receiving a request to write data;

writing the data to a disk; and

periodically executing disk-cache flush command.

2. The method of claim 1, further including appending each write operation to a first log to identify a storage location of data written to the disk subsystem.

Periodically generating a checkpoint that summarizes a content of the first log;

and Executing a flush command to store the checkpoint separate from the first log.

3. The method of claim 2, further including, in response to a crash, loading the checkpoint and scanning log entries to the first log that were generated after a most recent update to the checkpoint.

4. The method of claim 1, wherein the checkpoint is stored in a second log, separate from the first log.

5. The method of claim 1, wherein prior to generating the checkpoint, noting an end of the first log, and flushing the first log.

6. The method of claim 1, wherein the first log consists of a sequence of segments, the segments consist of a sequence of variable length stripes, a length of a stripe varies based on a quantity of disks addressed by a stripe.

7. The method of claim 1, wherein the periodically generating a checkpoint is performed at fixed time intervals.

8. The method of claim 1, wherein the periodically generating a checkpoint is performed at non-fixed time intervals.

9. A machine readable-medium having stored thereon a set of instruction, which when executed, perform a method of storing data that preserves an order of writes on a disk storage subsystem with write-back cache turned on, the method comprising:

receiving a request to write data;

writing the data to a disk; and

periodically executing disk-cache flush command.

10. The machine readable-medium of claim 9, further including appending each write operation to a first log to identify a storage location of data written to the disk subsystem.

Periodically generating a checkpoint that summarizes a content of the first log;

and Executing a flush command to store the checkpoint separate from the first log.

11. The machine readable-medium of claim 10, further including, in response to a crash, loading the checkpoint and scanning log entries to the first log that were generated after a most recent update to the checkpoint.

12. The machine readable-medium of claim 10, wherein the checkpoint is stored in a second log, separate from the first log.

13. The machine readable-medium of claim 10, wherein prior to generating the checkpoint, noting an end of the first log, and flushing the first log.

14. The machine readable-medium of claim 10, wherein the first log consists of a sequence of segments, the segments consist of a sequence of variable length stripes, a length of a stripe varies based on a quantity of disks addressed by a stripe.

15. The machine readable-medium of claim 10, wherein the periodically generating a checkpoint is performed at fixed time intervals.

16. The machine readable-medium of claim 10, wherein the periodically generating a checkpoint is performed at non-fixed time intervals.