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Recovery from errors in a redundant array of disk drives

a disk drive and array technology, applied in the field of redundant arrays of disk drives, can solve problems such as loss of fault tolerance to error conditions

Inactive Publication Date: 2000-08-29
IBM CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

In accordance with the invention, failures in a redundant array of disk drives is remedied by rebuilding the error-affected data using any one of a plurality of methods and apparatus any of which enable a continuing use of the disk drive array for information handling and data processing. Such rebuilding may use any or all of the methods and apparatus. A first method and apparatus is a variable rate rebuild which schedules rebuilds at a rate in a detected inverse ratio to a current or pending rate of disk drive usage or accessing within a parity group. Upon completing each scheduled rebuild, this method and apparatus also preferably takes advantage of any idle time of the array by continuing rebuild if there is no waiting access. A second method and apparatus effects rebuild during predetermined array idle times by starting a non-scheduled rebuild of a predetermined portion of the error-affected data. A third or opportunistic method and apparatus detects a need for a data rebuild during a usual access to the array. All three methods and apparatus are preferably used in conjunction with each other.

Problems solved by technology

Whenever one of the disk drives in a single-parity array fails, even though data can be successfully recovered, the fault tolerance to error conditions is lost.

Method used

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  • Recovery from errors in a redundant array of disk drives
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Embodiment Construction

Referring now more particularly to the appended drawing, like numerals indicate like parts and structural features in the various figures. Host processor(s) 10 (FIG. 1) are respectively connected to one or more controller(s) 11 by host to peripheral interconnection 12. A plurality of parity arrays 13, 14 and 15 are connected to controller 11 by a usual controller to peripheral device connection 17. Each of the FIG. 1 illustrated arrays 13-15 include five disk drives 20-24, no limitation thereto intended. Four of the disk drives 20-23 store like-sized blocks of data of one data unit. The block sizes may vary from data unit to data unit. A data unit can be an amalgamation of files, one file, graphic data, and the like. A fifth disk drive 24 is a parity or error detection redundancy storing drive P. The redundancy is a parity data block having the same size as the corresponding data blocks of the data unit. The redundancy is computed based upon any algorithm, including simple parity fo...

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PUM

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Abstract

Fault tolerance in a redundant array of disk drives is degraded when error conditions exist in the array. Several methods for rebuilding data of the array to remove the degradation are described. Data rebuilding for entire disk drives and partial data rebuilds of disk drives are described. All rebuild methods tend to reduce the negative affect of using array resources for the data rebuild. In one method rebuilding occurs during idle time of the array. In a second method rebuilding is interleaved between current data area accessing operations of the array at a rate which is inversely proportional to activity level of the array. In a third method, the data are rebuilt when a data area being accessed is a data area needing rebuilding.

Description

FIELD OF THE INVENTIONThe present invention relates to redundant arrays of disk drives, particularly to recovery from degraded redundancy by rebuilding data of error-affected tracks causing the degradation into spare tracks or disks.BACKGROUND OF THE INVENTIONPatterson et al in the article "A CASE FOR REDUNDANT ARRAYS OF INEXPENSIVE DISKS (RAID)", ACM 1988, Mar. 1988, describe several arrangements for using a plurality of data-storing disk drives. Various modes of operation are described; in one mode the data storage is divided among the several drives to effect a storage redundancy. Data to be stored is partially stored in a predetermined number of the disk drives in the array, at least one of the disk drives storing error detecting redundancies. For example, four of the disk drives may store data while a fifth disk drive may store parity based upon data stored in the four disk drives. Such a redundant array of disk drives may provide high data availability by introducing error det...

Claims

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Application Information

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Patent Type & Authority Patents(United States)
IPC IPC(8): G06F11/00G06F3/06G06F11/10G11B20/18
CPCG06F11/1092G11B20/1833G06F3/06
Inventor NG, SPENCER W.PALMER, DAVID W.THOMPSON, RICHARD S.
Owner IBM CORP
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