Error detection/correction and fault detection/recovery – Data processing system error or fault handling – Reliability and availability
Reexamination Certificate
1999-03-01
2001-11-20
Wright, Norman M. (Department: 2131)
Error detection/correction and fault detection/recovery
Data processing system error or fault handling
Reliability and availability
C711S114000
Reexamination Certificate
active
06321345
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to the transmission and storage of data and, more particularly, to managing response times in redundant arrays of inexpensive disks.
Digital video and television systems need high bandwidth data transmission and low latencies. Redundant arrays of inexpensive disks (RAID) support high bandwidth data transfers and very low latencies. RAID configurations employ redundancy and/or parity blocks to mask the failure of a disk.
RAID configurations divide a received data stream into a sequence of blocks and write consecutive blocks of the sequence to different disks in the array. To retrieve data, the RAID configuration reads the blocks from the disks of the array and reconstitutes the original data stream from the read blocks. To increase reception and transmission speeds, the RAID configuration may write to and read from the various disks of the array in parallel.
Individual disks of a RAID configuration will occasionally stall or respond slowly to an access request due to disk surface defects and bad block revectoring. During a slow response, the entire RAID configuration may wait while one disk transmits requested data. Thus, a single slowly responding disk can cause a long latency for a read operation from the RAID configuration.
For digital video and cable systems, one slowly responding disk can cause a disaster, because data needs to arrive at a video receiver at a substantially constant rate to keep the receiver's input buffer full. Continued long transmission latencies can deplete the input buffer. A receiver's input buffer is typically only large enough to store about 1 to 2 of video data, i.e. several megabytes of data. If a slow RAID configuration causes a transmission gap of longer than about 1 to 2, the receiver's input buffer may completely empty. If the receiver's input buffer empties, a viewer may perceive a noticeable pause in the video being viewed. Defect-free transmission of video requires that such pauses be absent.
RAID configurations are economically attractive, because they provide low latencies and high bandwidth data storage using inexpensive disks. But, contemporary inexpensive disks often have bad regions, which occasionally lead to bad block revectoring and slow disk responses. A bad region can cause a read, which normally lasts about 10 milliseconds (ms), to take 1,000 ms or more. Thus, slow responses can cause unpredictable read latencies. These latencies make RAID configurations less acceptable in video transmitters, because transmission latencies can lead to the above-discussed problems in video reception.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.
SUMMARY OF THE INVENTION
One object of the invention is to reduce the number of transmission gaps caused by slowly responding disks of a RAID configuration.
Another object of the invention is to provide a RAID configuration with predictable read latencies.
In a first aspect, the invention provides a RAID configuration. The RAID configuration includes a plurality of disks, a bus coupled to the disks to transmit data blocks, and a device to reconstruct a block stored in any one of the disks. The device reconstructs the block with associated data and parity blocks received from other disks. The device transmits the reconstructed block to a receiving device in response to one of the disks responding slowly.
In a second aspect, the invention provides a method of transmitting data from a RAID configuration. The method includes requesting that a first disk of the RAID configuration transmit a first block, reconstructing the first block from associated blocks stored in other disks of the RAID configuration, and transmitting the reconstructed first block directly to a receiving device. The step of transmitting is performed if the first disk does not complete transmission of the first data block within a predetermined time.
In a third aspect, the invention provides a RAID configuration, which stores parity and data blocks in stripes across the disks. The RAID configuration includes a plurality of disks and a processor connected to the disks. The processor is adapted to write a plurality of groups of associated data and parity blocks to the disks. The processor writes the data and parity blocks of each group to different ones of the disks and writes at least two blocks from different groups to one stripe.
In a fourth aspect, the invention provides a RAID configuration to transmit data blocks to a receiving device. The RAID configuration includes a plurality of disks, a processor to control reads from and writes to the disks, and a device to reconstruct blocks. The disks store blocks and transmit stored blocks to the receiving device. The processor determines if disks are slowly responding. The device reconstructs a block stored in a slowly responding one of the disks from associated blocks stored in the remaining disks if the processor determines that the one of the disks is slowly responding.
REFERENCES:
patent: 5754804 (1998-05-01), Cheselka et al.
patent: 5758057 (1998-05-01), Baba et al.
patent: 5862312 (1999-01-01), Mann et al.
“The RAIDBook, A Source Book for RAID Technology,” The RAID Advisory Board, p. 23 and 38, Jun. 1993.
Mann Bruce E.
Trasatti Philip J.
Ywoskus John A.
Fish & Richardson P.C.
Revak Christopher A.
Seachange Systems, Inc.
Wright Norman M.
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