Method and apparatus for RAID conversion

• US 7,334,156 B2
• Filed: 02/13/2004
• Issued: 02/19/2008
• Est. Priority Date: 02/13/2004
• Status: Active Grant

• Current Assignee: Tandberg Data Corporation
• Original Assignee: Tandberg Data Corporation
• Inventors: Dickson, Lawrence John, Land, Kris
• Primary Examiner(s): Beausoliel; Robert
• Assistant Examiner(s): Ehne; Charles
• Application Number:
  US10/779,378
• Publication Number:
  US 20050182992A1
• Time in Patent Office: 1,467 Days
• Field of Search: 714/6, 714/7
• US Class Current: 714/6.2
• CPC Class Codes: G06F 11/1096 Parity calculation or recalculation after configuration or reconfiguration of the system
• CPC Class Codes: G06F 2211/1004 Adaptive RAID, i.e. RAID system adapts to changing circumstances, e.g. RAID1 becomes RAID5 as disks fill up
• CPC Class Codes: G06F 3/0607 by facilitating the process of upgrading existing storage systems, e.g. for improving compatibility between host and storage device
• CPC Class Codes: G06F 3/0632 by initialisation or re-initialisation of storage systems
• CPC Class Codes: G06F 3/0689 Disk arrays, e.g. RAID, JBOD

Abstract

A general RAID conversion method is described for converting between different RAID configurations. The method includes reading a unit of user data from the source devices according to the source RAID algorithm, writing the user data together with redundant data (if any) to the target devices according to the target RAID algorithm, and from time to time releasing portions of the source devices containing data that has been converted. The conversion may be used to expand or contract the array, to increase or decrease usable capacity, and to increase or decrease the device-loss insurance level. Conversion may be performed on line (dynamically) or off line. The flexibility of the method allows the implementation of manual and/or rule-based RAID reconfiguration that automatically adjusts system parameters based on user request and/or a set of rules and conditions respectively. It may also be used to perform self-healing after one or more devices in the array have failed.

Claims

1. In a redundant array of inexpensive devices (RAID) comprising a controller and a plurality of storage devices for storing user data, the controller storing a plurality of RAID algorithms to be implemented for writing data to and reading data from the storage devices, a RAID conversion method for converting the away from a first RAID algorithm to a second RAID algorithm, comprising:

alternating between performing tasks in a conversion state and performing tasks in a user I/O state, wherein the tasks in the conversion state include;

(a) reading a unit of user data from the storage devices according to the first RAID algorithm;

(b) defining a watermark indicating the position where the data is read from the first RAID; and

(c) writing user data on appropriate storage devices according to the second RAID algorithm, wherein steps (a) and (c) are repeated to read and write data up to the watermark, and

wherein the tasks in the user I/O state include reading data from the storage devices upon user requests, wherein when requested data exist on both sides of the watermark, the requested data is read according to the second RAID algorithm before the watermark and according to the first RAID algorithm after the watermark; and

wherein the conversion state and user I/O state are repeated until all data on the storage devices are converted.

2. The method of claim 1, wherein the writing step includes writing updates to a semi-permanent cache.