Recovery from errors in a redundant array of disk drives

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...

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.

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