Error detection/correction and fault detection/recovery – Pulse or data error handling – Error/fault detection technique
Reexamination Certificate
1998-08-04
2001-08-07
Decady, Albert (Department: 2133)
Error detection/correction and fault detection/recovery
Pulse or data error handling
Error/fault detection technique
C714S770000
Reexamination Certificate
active
06272662
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is related to the following co-pending and commonly-assigned patent applications, all of which are filed on the same date herewith, and all of which are incorporated herein by reference in their entirety:
“System for Updating Data in a Multi-Adaptor Environment,” by Jai Menon, Divyesh Jadav, Deepak Kenchammana-Hosekote, Ser. No. 09/128,574;
“System For Changing The Parity Structure Of A Raid Array,” by Jai Menon and Divyesh Jadav, Deepak Kenchammana-Hosekote, Ser. No. 09/129,012;
“Updating And Reading Data And Parity Blocks In A Shared Disk System,” by Jai Menon, Ser. No. 09/129,067;
“Updating Data and Parity With and Without Read Caches,” by Jai Menon, Ser. No. 09/128,438; and
“Updating and Reading Data and Parity Blocks in a Shared Disk System with Request Forwarding,” by Jai Menon and Divyesh Jadav, Ser. No. 09/128,754.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a system for storing data in a shared storage device system.
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 Riegel, and Jim Wyllie, document no. 1063-6390 (IEEE 1995), which is incorporated herein by reference in its entirety.
One problem with the single storage subsystem is the risk of failure. Techniques have been developed to improve failback and recovery in case of failures in the hardware controller. One such failback technique is the Fast Write Technique which provides two separate controllers on different power boundaries that control the flow of data from host systems to DASDs. If one controller fails, the other controller can continue writing data to the DASD. Typically a non-volatile storage unit (NVS) is included with each separate controller, such that each NVS connected to a controller backs up the data the other controller is writing to DASD. Such failback systems employing the two-controller failsafe structure are described in U.S. Pat. Nos. 5,636,359, 5,437,022, 5,640,530, and 4,916,605, all of which are assigned to International Business Machines, Corporation (IBM), the assignee of the subject application, and all of which are incorporated herein by reference in their entirety.
RAID systems can also be implemented in a parallel computing architecture in which there is no central controller. Instead, a plurality of independent controllers that control local hard disk storage devices are separate nodes that function together in parallel to implement RAID storage methodologies across the combined storage space managed by each node. The nodes are connected via a network. Parity calculations can be made at each node, and not centrally. Such parallel RAID architecture is described in “The TickerTAIP Parallel RAID Architecture,” by Pei Cao, Swee Boon Lim, Shivakumar Venkatarman, and John Wilkes, published in ACM Transactions on Computer Systems, Vol. 12, No. 3, pgs. 236-269 (August, 1994), which is incorporated herein by reference in its entirety.
One challenge in shared disk systems implementing a parallel, shared disk RAID architecture is to provide a system for insuring that data is properly updated to disks in the system, that a write or update request invalidates stale data so such stale data is not returned, and that a read request returns the most current data.
SUMMARY OF THE INVENTION
To overcome the limitations in the prior art described above, preferred embodiments of the present invention disclose a system for performing an operation on a data block in a shared disk system. A first adaptor receives a request to perform an operation on a data block maintained in a data storage location. The first adaptor then determines whether the first adaptor controls access to the data block. The first adaptor performs the requested operation on the data block after determining that the first adaptor controls access to the data block. If the first adaptor does not control access to the data block, then the first adaptor transmits a first message to a second adaptor that controls access to the data block and requests control of access to the data block. After receiving the first message, the second adaptor transfers control of access to the data block to the first adaptor. The second adaptor then transmits a second message to the first adaptor that the first adaptor controls access to the data block. After receiving the second message, the first adaptor performs the requested operation on the data block.
In further embodiments, the requested operation is a write operation to update the data block associated with the lock unit. If the first adaptor controls access to the data block, then the first adaptor writes an update to the data block into a memory location and sets a lock state on the data block. If the second adaptor controls access, then the first adaptor must receive the second message before setting a lock state on the data block and writing the update to the data block into the memory location.
Further embodiments concern a read operation on a data block in a shared disk system. A first processing unit receives a read request for a data block maintained in a data storage location. The first processing unit then determines whether the first processing unit controls access to the data block. The first processing unit reads the data block after determining that the first processing unit controls access to the data block. Upon determining that the first processing unit does not control access to the data block, the first processing unit obtains control of the data block and performs the requested read operation on the data block.
With the preferred embodiments, access to data blocks is controlled. Controlling access helps insure that parity updates are properly handled, data in memory locations is invalidated so that stale or outdated data is not returned to a later read request, stale data is not destaged to a storage device, and a read request returns the latest version of the data block.
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Jadav Divyesh
Menon Jaishankar Moothedath
Voruganti Kaladhar
Altera Law Group LLC
Chase Shelly A
De'cady Albert
International Business Machines - Corporation
Merchant, Gould, Smith, Edell, Welter & Schmidt
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