Error detection/correction and fault detection/recovery – Pulse or data error handling – Error/fault detection technique
Reexamination Certificate
1998-08-04
2001-08-21
Decady, Albert (Department: 2133)
Error detection/correction and fault detection/recovery
Pulse or data error handling
Error/fault detection technique
C714S770000, C711S114000
Reexamination Certificate
active
06279138
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a system for changing the parity structure of data in a shared storage device system and, in particular, altering the parity structure of a RAID array.
2. Description of the Related Art
In Redundant Arrays of Independent Disks (RAID) systems, data files and related parity are striped across multiple disk drives. In storage subsystems which manage numerous hard disk drives as a single direct access storage device (DASD), the RAID logic is implemented in the controller of the subsystem. RAID storage methodologies have also been implemented in software for execution on a single host computer. This allows the single host computer, such as a personal computer, to implement RAID storage techniques on local hard disk drive space. Such software RAID methodologies are described in “Algorithms for Software and Low Cost Hardware RAIDs,” by Jai Menon, Jeff Reigel, and Jim Wyllie, Document No. 1063-6390/95, pgs. 411-418 (IEEE 1995).
One technique for altering the arrangement of logical drives in a storage subsystem requires that the RAID array to be taken off-line to back-up the data in order to delete the logical drive or array, create new logical drives/arrays, format the storage space, and then, finally, restore the data. The PC ServeRAID SCSI adaptor from International Business Machines Corporation (“IBM®”), the assignee of the present patent application, offers logical drive migration (LDM). “IBM” is a registered trademark of IBM, and “ServeRAID” is a trademark of IBM. The LDM feature allows a single IBM PC ServeRAID SCSI adaptor to alter the structure of a RAID array by altering the RAID level or adding or removing a storage device, e.g., hard disk drive, to increase or decrease the size of the current array. Integrating one or more new hard disks into an existing array increases the size of all logical drives in the array. The IBM PC ServeRAID SCSI adaptor can concurrently service input/output requests to data in the RAID array involved in logical drive migration (LDM) activities, i.e., having their RAID level changed or distributing the current RAID level across a different number of disk drives.
As networks increase in size, an adaptor can be overburdened with I/O requests to a storage device managed by the adaptor. Moreover, if the IBM PC ServeRAID SCSI adaptor is performing logical drive migration (LDM) activities, the adaptor will take longer to service I/O requests to the storage device.
SUMMARY OF THE INVENTION
To overcome the limitations in the prior art described above, preferred embodiments of the present invention disclose a system for altering the structure of parity groups. A parity group consists of a set of data blocks and parity data for the data blocks. The data and parity data are stored in at least two storage devices. For each N, wherein N is an integer value greater than or equal to zero, a first processing unit alters the parity structure of the Nth set of parity groups. A set of parity groups includes at least one parity group. A second processing unit determines an Nth range of parity groups including the Nth set of parity groups. Upon the second processing unit detecting the failure of the first processing unit while altering the parity structure of the parity groups in the Nth set, the second processing unit processes the parity groups in the determined Nth range to determine a parity group whose parity structure was being altered when the first processing unit failed.
In further embodiments, altering the parity structure comprises at least one of: changing the RAID level of the parity structure, adding a storage device to increase the storage capacity, and removing a storage device to decrease the storage capacity.
In yet further embodiments, should the first processing unit fail, the second processing unit alters the parity structure for the determined parity group whose parity structure was being altered when the first processing unit failed and parity groups whose parity structure was not altered by the first processing unit.
The preferred embodiments provide a system of at least two adaptors involved in altering the parity structure of a data array, such as a RAID array. In preferred embodiments, the adaptor not changing the parity structure, e.g., the secondary adaptor, as well as the adaptor changing the parity structure, e.g., the primary adaptor, can handle input/output requests to the data array. Moreover, with the preferred embodiments, the secondary adaptor knows within a range how far the primary adaptor progressed in altering the parity structure of parity groups. The secondary adaptor can complete altering the structure of the parity groups based on such information when the primary adaptor fails.
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Jadav Divyesh
Kenchammana-Hosekote Deepak R.
Menon Jaishankar Moothedath
Altera Law Group LLC
De'cady Albert
International Business Machines - Corporation
Merchant, Gould, Smith, Edell, Welter & Schmidt
Ton David
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