|Publication number||US6950966 B2|
|Application number||US 09/907,534|
|Publication date||Sep 27, 2005|
|Filing date||Jul 17, 2001|
|Priority date||Jul 17, 2001|
|Also published as||CA2454061A1, EP1417581A2, US20030016596, WO2003009124A2, WO2003009124A3|
|Publication number||09907534, 907534, US 6950966 B2, US 6950966B2, US-B2-6950966, US6950966 B2, US6950966B2|
|Inventors||Kenneth F. Chiquoine, Bruce Mann, Michael D. Raspuzzi, Philip J. Trasatti|
|Original Assignee||Seachange International, Inc.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (28), Non-Patent Citations (8), Referenced by (23), Classifications (13), Legal Events (5)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This invention relates generally to the transmission and storage of data on RAID devices and clustered computer systems.
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 storage uses redundancy and/or parity blocks to mask the failure of a disk. RAID arrays have limited capacity to handle failures due to fixed reconstruction cache size.
RAID storage divides 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 blocks are read from the disks of the array and are reconstituted into the original data stream from the read blocks. To increase reception and transmission speeds, the various disks of the array of the RAID storage may be written to and read from in parallel.
Individual disks of a RAID storage configuration will occasionally stall or respond slowly to an access request due to disk surface defects and bad block re-vectoring. Another problem occurs when a drive is being rebuilt or reconstructed from information on other drives. 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. If a slow RAID configuration causes a transmission gap so that 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.
According to an aspect of the invention, a method for reading data from a clustered system of a plurality of redundant array of inexpensive disks (RAID) device configurations includes receiving a message from a requesting one of members of the clustered system that indicates a next location for a particular block for a subsequent read operation from a drive in the RAID device and returning to the requesting one of members of the clustered system a hint that indicates the state of the drive in the RAID device corresponding to location for the subsequent read operation.
According to an additional aspect of the invention, a clustered system of a plurality of redundant array of inexpensive disks (RAID) configurations to transmit data blocks to a receiving device includes a plurality of cluster members coupled so that any one cluster member can deliver data to at least some of remaining cluster members. Each cluster member includes a plurality of disks adapted to store the blocks and to transmit the stored blocks to the receiving device and a processor to control reads from and writes to the plurality of disks. The member also includes a process to receive a message that indicates a next location for a particular block for a subsequent read operation from a drive in the RAID device and produce a hint that indicates the state of the drive in the RAID device corresponding to location for the subsequent read operation.
According to an additional aspect of the invention, a clustered configuration includes a plurality of clustered nodes each node comprising a redundant array of inexpensive disks (RAID) and a processor adapted to write blocks to and read blocks from the arrays and a process to receive a message that indicates a next location for a particular block for a subsequent read operation from a drive in the redundant arrays of inexpensive disks of one of the nodes and produce a hint that indicates the state of the drive in the redundant arrays of inexpensive disks corresponding to location for the subsequent read operation.
One or more of the following advantages may be provided by one or more aspects of the present invention.
A clustered system includes a plurality of cluster members. When the clustered system requests data from a RAID configuration of one of the cluster members, a message is return that indicates the state of the member on the next read for a particular block. This message or hint can indicate that reading a particular block will be slow or that the device is degraded or unavailable. When the system reads the particular block, the system will skip the bad drive and instead read the parity and data block from the other drives. A reconstructor performs an XOR operation on parity and data to reconstruct the missing data corresponding to the bad or reconstructing drive. Thus, by skipping the bad drive and not waiting for a slow or degraded node or drive to respond before trying to reconstruct data improves the performance of the RAID array while in degraded state such that performance of the RAID array approaches or reaches normal performance.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.
The processor 20 also includes a reconstructor 22. In some embodiments, the processor 20 is programmed to provide the reconstructor 22. In other embodiments, the reconstructor 22 is implemented as a coprocessor, as discussed below.
The processor 20 transmits data blocks over an interface or line 17, for example, a bus or a cable, airwaves, and so forth to a requesting device 19. The processor 20 executes a process 40 to produce a hint for use by the processor 20 or in some embodiments, a remote receiving device (e.g., receiving device 19) to indicate that a request for data may be directed to a disk that is bad or will have a slow response. The file system (described below) executes on processor 20 has knowledge of how data is stored on disk drives. The file system has a mapping of data blocks to disk storage locations. The disk controller (not shown) returns a message to the file system indicating the state of the disk drives. With the knowledge of the mapping and message pertaining to the state of the disk drives, the file system can produce the hint to the processor 20 or a requesting system 19, as the case may be. The processor 20 or requesting system 19 determines whether to read the block from the drive or initiate a recovery mode and read the corresponding parity block and data from other drives, thus avoiding the bad drive. Software components 70 including the file system are described in FIG. 6.
A first processor, e.g., processor 20 receives consecutive groups of pairs of data blocks and generates a parity block to associate with each pair of data blocks. The first processor 20 sends one block from each associated group of three blocks to each of RAID configurations 12, 12′, 12″. Each processor 20, 20′, 20″ of the respective RAID configuration 12, 12′, 12″ subsequently breaks each block into two mini-blocks and generates a parity mini-block to associate with the two miniblocks. Each second level RAID configuration 12, 12′, 12″ stores the mini-blocks as illustrated in
Still referring to
The cluster 10 uses a RAID process to build a fault tolerant clustered system of single processors. Data objects are stored as named fragment files across the members of the cluster. Data objects are striped in accordance with RAID-5 process (or other process, e.g., RAID-4) and stored with parity information to allow a missing named fragment file to be reconstructed if a cluster member (node) 11 fails.
The configuration shown in
The processor 64 performs an exclusive OR (XOR) of the associated parity and data blocks to reconstruct the data block of the stalled one of configurations 12-12″. To perform the XOR, the processor 64 reads the associated blocks from the memory device 62. The processor 64 XOR's corresponding bits of the read associated parity and data blocks in a byte-by-byte manner. The processor 64 writes the results of the XOR back to the memory device 62 for transmission to the appropriate one of the receiving devices 39-39″. The reconstructor 22 can produce a reconstructed block for any one of the configurations 12-12″.
Referring now to
In order to provide transparent data object access, a RAID port driver masks that the data object exist as a set of named fragment files. The port driver provides multiplexing and demultiplexing services to merge named fragment files into a data stream. The RAID port driver registers as both a provider and a consumer. When the class driver attempts to open a data object, it calls all of the provider port drivers in the system. Upon being called, the RAID port driver becomes a consumer and uses the class driver to open each of the data fragments that comprise the data object. Once a session has been established to each of the named fragment files, that is, once access has been provided to each named fragment file, the RAID port driver performs an open call back to notify the class driver that the data object is available.
In the particular application of accessing the data (e.g., video) objects, the port driver accesses the data (video) objects stored on the cluster. The remote file provider represents any third party application or device driver that might use the cluster technology. The on-disk structure of the cluster volume (file system 54) can be either NTFS, FAT, SeaFile or raw disk access. The file system component is responsible for storing and retrieving the named fragment files.
The processor 20 (
The read-ahead message is used to show where the parity is. When the previous I/O transaction has completed, the file system on the processor 20 has communicated with the RAID controller (not shown) and has determined if the next block would be valid (e.g., available from the RAID controller, will respond in time, and so forth) or not. The file system on the processor 20 indicates via, the hint message, if the next block will be valid or invalid. If invalid, the file system returns the hint to the requesting processor 20, 20′ 20″ indicating that the next block will be a delayed read or will not be available, etc. This will enable the requesting one of configurations 12-12″ to initiate a read around the bad block, i.e., to forgo a subsequent read request to the bad drive and rather to request parity and data from good drives.
The hint message can indicate a “next bad byte offset.” The next bad byte offset indicates where the bad block is located based on some offset. The requesting system receives the “next bad byte offset” and can determine that the RAID array has a bad or reconstructing drive. The requesting system will skip the drive and instead read the parity and data block from the other drives. The reconstructor 22 performs an XOR operation on parity and data to reconstruct the missing data corresponding to the bad or reconstructing drive. Thus, by skipping the bad drive and not waiting for a slow drive to respond before trying to reconstruct data, will improve the performance of the RAID array towards normal performance.
Returning of the hint instructs the requesting system to start the recovery process or requesting process without waiting for degradation of performance to occur. The processor 20 through the file system has intimate knowledge of the block mapping and file structure on the RAID configuration 11 and the disk drives 14 a- 14 c. Thus, the processor 20 can examine the request address and a stored block map (not shown) that indicates where the blocks are stored on the disk drives 31-33. From that information the file system constructs the hint to send to a device that will request the bad block to indicate the state of the RAID array. The hint masks various failures of the RAID array.
Nodes 11, 11′ and 11″ in the cluster 10 are peer-to-peer, consuming and providing data to the clustered system 10. The hint improves the performance of an impaired disk subsystem. When a drive is dead or rebuilding in a RAID array, the processor 20 needs to read the entire stripe row to reconstruct the data missing on the failed drive. When a large number of reader threads is placed on a degraded RAID array, the reconstruction cache is purged as new requests are serviced. Because the RAID array has a fixed size reconstruction cache, some/all data blocks may need to be read twice because they are flushed before they are used to reconstruct the bad block. The performance of the RAID controller will degrade to ½ or more of the non-degraded performance in this case. By using the hint message to avoid the failed drive, the impaired RAID array can run at 11/12 th efficiency (assuming a 12 drive array). The input/output requests from the failed drive are handled by the other systems in the cluster in the form of parity data requests ( 1/12 th of the load on the RAID array).
The process 100 reconstructs the block from parity and data as discussed above. With the hint indicating a bad read, the read ahead is turned off, because performing such a read operation will degrade system 10 performance. The read ahead cache (not shown) is disabled at the point that the file system returns the hint to the requesting system indicating the next request at the byte offset will land on a bad drive.
In other embodiments the file system 74 can look further ahead and produce a hint to the remote system 19 where the next request to the bad drive is going to land, so that the requesting system 11 can read up to that point and skip over the bad drive. The local file system 74 on the processor 20 manages the file fragment at the remote end and knows that the next block in the file is either bad or good. The file system 74 returns the hint to the requesting system 11. The requesting system 19 determines whether to read the block from the drive or initiate a recovery mode and read the parity block and data from other drives and Exclusive-Or the data with parity to recover the lost block.
In a case where the file system 74 encounters the same situation with two systems, the file system 74 can implement a tie-breaking algorithm, e.g., a round robin algorithm where the system 10 first reads one node and the next time reads from the other node.
Referring back to
The video transmission system 150 can lower the occurrence of viewing pauses by transmitting a reconstructed data block in response to receiving the hint. In one embodiment of the system 150, the RAID configuration 11 in system 10 needs about 100 ms to transmit and reconstruct a data block. The receiver's input data buffer 117 stores about 2000 ms of video data. This storage provides sufficient stored data to deliver normal video while giving sufficient time to reconstruct lost data in response to receiving the hint.
Other embodiments are within the scope of the appended claims.
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|U.S. Classification||714/42, 714/E11.034, 714/6.13|
|International Classification||G06F11/00, H04L1/22, H04N5/00, G06F3/06, G06F11/10|
|Cooperative Classification||G06F2211/1028, G06F11/1076, G06F11/1088|
|European Classification||G06F11/10R, G06F11/10R3|
|Oct 26, 2001||AS||Assignment|
Owner name: CITIZENS BANK OF MASSACHUSETTS, MASSACHUSETTS
Free format text: SECURITY INTEREST;ASSIGNOR:SEACHANGE INTERNATIONAL, INC.;REEL/FRAME:012333/0977
Effective date: 20011022
|Dec 3, 2001||AS||Assignment|
Owner name: SEACHANGE INTERNATIONAL INC., MASSACHUSETTS
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:CHIQUOINE, KENNETH F.;MANN, BRUCE;RASPUZZI, MICHAEL D.;AND OTHERS;REEL/FRAME:012439/0949
Effective date: 20011127
|Mar 7, 2006||CC||Certificate of correction|
|Oct 1, 2008||FPAY||Fee payment|
Year of fee payment: 4
|Feb 25, 2013||FPAY||Fee payment|
Year of fee payment: 8