Abstract:
Various apparatus and methods for controlling data for a redundant array of inexpensive/independent disks (RAID) are presented. For example, in one illustrative embodiment, a controlling apparatus can include a translation device capable of reading data from a plurality of N disks, wherein the data of the N disks has a format consisting of a sequence of block stripes with each block containing one or more sector stripes, and wherein each sector stripe is formatted such that N−1 of the sectors contain contiguous target data and the remaining sector contains parity data for the other N−1 target data sectors.

Description:
FIELD OF THE DISCLOSURE 
     This disclosure pertains to the field of high-speed and reliable disk storage systems. 
     BACKGROUND 
     In the data storage arts, the term “RAID” stands for a “redundant array of inexpensive disks” (or alternatively a “redundant array of independent disks”) and refers to a system that uses multiple hard drives to share or replicate data. In its original implementations, the key advantage to a RAID system was the ability to combine multiple low-cost devices using older technology into a storage disk array that offered greater performance than what was affordably available in a single device using the newest technology. Depending on the RAID version chosen, the benefits of RAID systems include (as compared to single drives) one or more of increased data integrity, fault-tolerance, throughput and capacity. 
     A RAID system is typically used on server computers, and is usually (but not necessarily) implemented with identically-sized disks. However, with decreases in hard drive prices and wider availability of RAID options built into motherboard chipsets, RAID is also being found and offered as an option in more advanced personal computers. This is especially true in computers dedicated to storage-intensive tasks, such as video and audio editing. 
     Two particular RAID levels of interest, known as RAID 4 and RAID 5, operate by distributing data over a plurality of disk with redundant parity information assigned to a single disk (RAID 4) or distributed among the various disks (RAID 5). Some of the primary advantages to RAID 4 and RAID 5 systems are that large amounts of data can be quickly offloaded to external devices while the failure of a single disk could be handled albeit with some performance degradation. 
     Unfortunately, when a disk does fail in a RAID 4 or RAID 5 system, it is necessary to replace the failed disk and reconstruct the lost data using the remaining disks, a task that can be very difficult if the RAID is busy delivering large amounts of data over long periods of time, and very important as the loss of another disk in the interim would mean a loss of all of the data on the RAID system. Further, present RAID 4 and RAID 5 systems are not well suited for high-speed streaming data, especially in the event of a failure. Thus, new technology related to improving RAID performance is desirable. 
     SUMMARY 
     In an illustrative embodiment, an apparatus for controlling data for a redundant array of inexpensive/independent disks (RAID) includes a translation device capable of reading data from a plurality of N disks, wherein the data of the N disks has a format consisting of a sequence of block stripes with each block containing one or more sector stripes, and wherein each sector stripe is formatted such that N−1 of the sectors contain contiguous data and the remaining sector contains parity data for the other N−1 sectors. 
     In another embodiment, a system for storing and retrieving data includes a plurality of N disks, wherein data of the N disks has a format consisting of a sequence of block stripes with each block containing one or more sector stripes, and wherein each sector stripe is formatted such that N−1 of the sectors contain contiguous data, and the remaining sector contains parity data for the other N−1 sectors. 
     In yet another embodiment, a method for storing a stream of data on a redundant array of inexpensive/independent disks (RAID) includes separating the stream of data into blocks of data with each block containing (N−1)×M sectors of data, where N is the number of disks in the RAID and M is an integer greater than zero, organizing each block of data into M sub-blocks with each sub-block having (N−1) sectors of contiguous data, and for each sub-block of data, storing the sub-block&#39;s sectors into a respective disk of the RAID to create a sector stripe. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The example embodiments are best understood from the following detailed description when read with the accompanying drawing figures. It is emphasized that the various features are not necessarily drawn to scale. In fact, the dimensions may be arbitrarily increased or decreased for clarity of discussion. Wherever applicable and practical, like reference numerals refer to like elements. 
         FIG. 1  is an exemplary system using a RAID storage system; 
         FIG. 2  depicts data storage on both a conventional RAID system as well as on an improved RAID system according to the present disclosure; 
         FIG. 3  is a portion of an exemplary RAID controller according to the present disclosure; 
         FIG. 4  is a flowchart outlining an exemplary data storage procedure according to the present disclosure; 
         FIG. 5  is a flowchart outlining an exemplary data retrieval procedure according to the present disclosure; 
         FIG. 6  is a flowchart outlining an exemplary data retrieval and rebuilding procedure according to the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, for purposes of explanation and not limitation, example embodiments disclosing specific details are set forth in order to provide a thorough understanding of an embodiment according to the present teachings. However, it will be apparent to one having ordinary skill in the art having had the benefit of the present disclosure that other embodiments according to the present teachings that depart from the specific details disclosed herein remain within the scope of the appended claims. Moreover, descriptions of well-known apparatus and methods may be omitted so as to not obscure the description of the example embodiments. Such methods and apparatus are clearly within the scope of the present teachings. 
     The example embodiments are best understood from the following detailed description when read with the accompanying drawing figures. It is emphasized that the various features are not necessarily drawn to scale. In fact, the dimensions may be arbitrarily increased or decreased for clarity of discussion. Wherever applicable and practical, like reference numerals refer to like elements. 
     The various advantages offered by the disclosed methods and systems include providing an improved RAID controller that is not only less expensive but that offers a performance increase of several times that of conventional RAID systems. For example, an eight (8)-disk RAID 5 system using an exemplary controller can not only simultaneously provide eight separate MPEG data streams to the outside world, but the effects of a single disk failure is typically limited to less than a few milliseconds of interrupted data, after which the RAID system will perform as before. Further, upon replacement of the failed disk, the exemplary RAID controller can perform data reconstruction on the replacement disk again without interrupting the eight outbound MPEG data streams. Accordingly, while the disclosed RAID systems can be used for practically any use, their advantages are particularly prominent when used to store and retrieve streaming data such as MPEG data, other video data, music, animations, background scenes for games and so on. 
     For the purpose of this disclosure the term “block stripe” (and its derivatives) shall refer to its commonly known meaning in the RAID storage arts as a data structure having multiples segments spanning multiple disks. 
     Further the term “sector stripe” shall refer to a data structure of related data being of one sector in depth and spanning multiple disks. See,  FIG. 2  for examples of sector stripes S 1 , S 2  and S 3 . 
     Still further, the term “target data” shall refer to some data content to be received from an external source and stored and/or stored to be delivered to an external device, such as an MPEG data stream. Target data does not by itself generally affect the operation of a disk. 
     Also, the term “parity data” shall refer to its commonly known meaning in the RAID storage arts as the XOR product of multiple bytes, segments, blocks and so on. 
       FIG. 1  is an exemplary system  100  using RAID-based storage technology. As shown in  FIG. 2 , the exemplary system  100  includes a data source/sink  150  coupled to a RAID storage system  110 . The exemplary RAID storage system  110 , in turn, includes four hard disks  120 - 126  controlled by a common disk controller  112 . 
     In a first mode of operation, the data source/sink  110  can provide target data to the RAID storage system  110  upon which the disk controller  112  can receive the data and divide the received data into separate blocks. In the present embodiment where four disks  120 - 126  are used, a parity sector is generated for every three target data sectors in a block to produce a separate “stripe” of four sectors. Then each stripe of sectors is used to form part of a stripe of blocks stored in the various disks  120 - 126 . Depending on whether a RAID 4 or a RAID 5 system is specified, the disk controller  112  will store the parity blocks on a single disk  120 - 122 ,  124  or  126  or distribute the parity blocks among the four disks  120 - 126 . 
     The exemplary disk controller  112  can store data in the disks  120 - 126  according to a modified format (compared to conventional RAID systems) that can increase data throughput while decreasing internal memory requirements. 
     For example,  FIG. 2  depicts the differences between the way data is stored in a conventional RAID system  210  as compared to the modified RAID storage format used in an exemplary RAID system  220 . As shown in  FIG. 2 , for both systems  210  and  220 , each stripe of blocks consists of nine (9) target data sectors and three (3) parity data sectors. Also, as the exemplary two systems  210  and  220  are representative of RAID 5 architecture, the various parity sectors P 0 -P 11  are distributed/rotated among the four disks  120 - 126  as a function of block number/location. 
     As also shown in  FIG. 2  (on the bottom left) for the conventional storage system  210 , the nine target data sectors D 0 -D 8  of block stripe A are organized in groups of contiguous data {D 0 ,D 1 ,D 2 }, {D 3 ,D 4 ,D 5 } and {D 6 ,D 7 ,D 8 } respectively located on disks  120 ,  122  and  124  with disk  126  containing parity data sectors {P 0 , P 1 , P 2 }. A similar organization is shown for block stripes B, C and D with parity data shifting to disks  124 ,  122  and  120  respectively. The consequence of this data organizations is that while data is contiguous on a per-disk basis, the data is non-contiguous for any given sector stripe. 
     For example, the three sector stripes S 1 , S 2  and S 3  of block stripe A data are arranged in groups having non-contiguous target data sectors {D 0 ,D 3 ,D 6 ,P 0 }, {D 1 ,D 4 ,D 7 ,P 1 } and {D 2 ,D 5 ,D 8 ,P 2 } with parity sector P 0  being derived by non-contiguous data sectors D 0 , D 4  and D 7 , parity sector P 1  being derived by non-contiguous data sectors D 1 , D 5  and D 8 , and parity sector P 2  being derived by non-contiguous data sectors D 2 , D 6  and D 9 . Similar consequences are found for block stripes B, C and D. 
     In contrast to the storage technique used for conventional RAID 4 and RAID 5 systems, the modified storage system  220  (bottom right) organizes data non-contiguously along disk boundaries but contiguously along the sector stripes. Accordingly, sector stripes S 1 , S 2  and S 3  are grouped into contiguous target data sectors {D 0 ,D 1 ,D 2 ,P 0 }, {D 3 ,D 4 ,D 5 ,P 1 } and {D 6 ,D 7 ,D 8 ,P 2 } respectively. Further, parity sector P 0  is derived from contiguous data sectors D 0 -D 2 , parity sector P 1  is derived from contiguous data sectors D 3 -D 5 , and parity sector P 2  is derived from contiguous data sectors D 6 -D 8 . 
     The format of the modified system  220  gives rise to several advantages. The first advantage is that contiguous data can be read faster from the disks  120 - 126  in smaller increments while still checking parity. That is, in order to read contiguous data sectors D 0 -D 2 , a RAID controller may take three times the amount of time using the conventional system  210  as with the modified system. 
     Further, for situations where all nine data sectors D 0 -D 8  must be provided in their natural order (e.g., for certain high-speed applications, such as providing MPEG streams), contiguous data sectors can be extracted using a memory buffer having one-third the size of conventional systems by serially uploading stripes S 1 , S 2  and S 3 —one at a time—before forwarding the data off system. 
     Still further, data uploading and reconstruction after a disk failure may be simultaneously performed a sector stripe at a time with little or no impact on data delivery performance, and parity information may be more easily derived. 
     Returning to  FIG. 1 , in a second mode of operation the RAID storage system  110  can upload target data from its disks  120 - 126 , and deliver the uploaded data to the data source/sink  150 . In this retrieval/read mode, the disk controller  112 , after receiving a data retrieval/read request from the data source/sink  150 , can direct the various disks  120 - 126  to simultaneously recall the requested data from the appropriate sector stripes on the disks  120 - 126 . Again, referring to  FIG. 2 , given that the position of a parity sector may vary as a function of block number/position the disk controller  112  may need to determine which disk  120 - 126  contains parity information, and either upload only the target data-bearing sectors (one sector stripe at a time) or optionally upload the entire sector stripe including parity data. 
     Depending on the embodiment, the disk controller  112  can store both target data and parity data in a block of RAM, then perform a parity check from the RAM. The parity check results for each sector stripe can then be forwarded to the source/sink  150 . 
     Alternatively, the disk controller  112  can forego any parity check and simply provide the target data to the source/sink  150 . 
     In addition to the standard read mode described above, the exemplary disk controller  112  can use an alternative read mode, sometimes referred to as the “degraded mode” of a RAID system. In the degraded mode, one of the disks  120 - 126  is assumed to have failed. However, because of the redundant information provided by the parity sectors, the data of each sector stripe can be faithfully reconstructed, and the reconstructed data can be forwarded to the data source/sink  150  along with the target data. 
     It should be appreciated that in a RAID 4 or RAID 5 system, the degraded mode and/or the rebuilding time necessary to recreate data onto a replacement disk is considered the window at which the RAID array is most vulnerable to data loss. During this time, if a second disk failure occurs, data is unrecoverable. 
     Conventional RAID controlling systems typically use some form of software solution to handle degraded operational modes or rebuilding—either relying on the host processor of a server or personal computer or a special embedded processor on a “hardware solution” board, to perform data reconstruction. 
     In contrast, the exemplary RAID processor  112  takes a gate-level hardware approach to reconstructing lost data. Because of the gate-level solution, data reconstruction can take literally but a few clock cycles, as opposed to the hundreds of clock cycles for software approaches or pseudo-hardware (i.e., embedded processor) approaches. 
     Because of the gate-level hardware approach to data reconstruction, the disk controller  112  suffers little or no appreciable loss of performance due to a disk failure due to the negligible added overhead. This approach not only allows the correct data to be passed to the data source/sink  150 , but also allows the disk controller  112  to reconstruct data on a failed disk while simultaneously providing target data to the outside world. 
     Further, because of the lower memory requirements due to the use of contiguous data sector stripes, overall costs of the added gate-level parity checking are balanced with the lowered costs of using smaller memory buffers. 
       FIG. 3  is a portion of an exemplary RAID disk controller  112  according to the present disclosure capable of controlling a RAID array of N disks. As shown in  FIG. 3 , the RAID disk controller  112  includes a controller  310 , a memory  320 , state control logic  330 , a synchronization device  340 , a target data sector forming/extraction device  350 , a parity sector processing device  360 , a translation device  370 , a ping-pong data buffer  380  and an input/output device  390 . 
     Although the exemplary RAID disk controller  112  of  FIG. 3  uses a bussed architecture, it should be appreciated that any other architecture may be used as is well known to those of ordinary skill in the art. For example, in various embodiments, the various components  310 - 390  can take the form of separate electronic components coupled together via a series of separate busses, or alternatively a collection of dedicated logic arranged in a highly specialized architecture and implemented with gate-level logic. 
     It also should be appreciated that some of the above-listed components  330 - 370  can take the form of software/firmware routines residing in memory  320  and be capable of being executed by the controller  310 , or even software/firmware routines residing in separate memories in separate servers/computers being executed by different controllers. 
     Returning to  FIG. 3 , components  330 - 380  can be conceptually grouped into what can be referred to as an “encoder/decoder”, i.e., a device that organizes data on a collection of RAID disks. While in various embodiments an encoder/decoder may be an amalgam of nearly endless combinations of hardware and software, it should be appreciated that, as discussed above, by implementing key portions of the exemplary translator as gate-level hardware solutions, performance can be greatly improved. 
     In operation and under control of the state control logic  330 , the synchronization device  340  can start and synchronize the N number of disks controlled by the disk controller  112 . 
     For incoming target data to be written onto the disks, the target sector forming/extraction device  350  can receive the target data from the input/output device  390 , and break the target data into contiguous portions that could be accommodated by (N−1) sectors. Again as noted above, when insufficient target data is available, some sectors may be padded with zeros. The target sector forming/extraction device  350  may also add header information, checksums and other information to each sector as may be necessary or desired. Note that the target sectors can be formed and modified in one of the ping-pong data buffers  380 . 
     Simultaneously, the translation device  370  can determine where the current target data sectors formed by the target sector forming/extraction device  350  are to be written within the RAID systems&#39; disks, and which of the N disk should contain parity information. 
     Using the N−1 sectors of data formed by the target sector forming/extraction device  350 , the parity sector processing device  360  can generate a complementary parity sector. For the present embodiment, the parity sector processing device  360  is implemented with gate-level hardware such that the parity sector can be generated in as little as a single clock cycle, which represents significant performance improvement over known systems. As with the target data sectors, each parity sector may be calculated ‘on the fly’ from the Data Sector&#39;s passing through the encoder sector unit buffer. Notably, the encoder and decoder can operate simultaneously. 
     Once all sectors of a sector stripe are appropriately formed in one of the ping-pong data buffers  380 , the translation device  370  can cause the appropriate ping-pong data buffer  380  to deliver the sector stripe of data to the N disks for simultaneous storage. 
     By repeating the various processes described above, the various components  330 - 380  of the encoder/decoder can form a pattern of sector stripes consistent with the sector layout shown in  FIG. 2 . 
     While read operations are obviously quite different from write operations, the same general components  330 - 380  can nonetheless be used. During a read operation, the state control logic  330  can cause the translation device  370  to determine the block stripe and sector stripe locations of some data of interest. Subsequently, the state control logic  330  can cause the ping-pong data buffers  380  to load the appropriate sector stripes one after the other. After each sector stripe is fully uploaded, the parity sector processing device can perform a parity check to determine data integrity while the target data forming/extraction device  350  can extract the target data, which can be offloaded to an intended location via the input/output device  390 . 
     In situations where a sector is determined to hold bad data (e.g., via a bad checksum or a failure status flag from one of the N drives), the exemplary encoder/decoder can employ the parity sector processing device  360  to reconstruct either the missing target data or parity data. The target data could then be offloaded. Should a replacement disk be provided for the failed disk, reconstructed data sectors could be written to the replacement disk even in situations where multiple streams of data are being uploaded and delivered to an external device. 
       FIG. 4  is a flowchart outlining an exemplary data storage procedure for a RAID system according to the present disclosure. The process starts in step  402  where the RAID system is started and its disks synchronized. Then, in step  410 , a determination is made as to whether a request has been made to write data to the RAID. If a write request has been made, control continues to step  420 ; otherwise, control jumps to step  412  where the process waits for a next request (read, write or otherwise) and a subsequent write determination in step  410  is made. 
     In step  420 , the RAID system can receive incoming data. Next, in step  422 , the received target data is divided into contiguous sections. Then, in step  424 , the contiguous sections of data can be used to create an appropriate number of contiguous sectors for a sector stripe. Zero padding of the sectors may be used if insufficient data is available to create an entire sector stripe. Control continues to step  426 . 
     In step  426 , a parity sector is created based on the sectors of step  424 . Then, in step  428 , the sectors can be assigned to an appropriate disk, which for a RAID 4 system would be a single predetermined disk and for a RAID 5 system would be determined as a function of block stripe number/location. Then, in step  430 , a sector stripe can be written to the RAID disks in a manner consistent with the modified system  220  of  FIG. 2 . Control continues to step  440 . 
     In step  440 , a determination is made as to whether there is more data to be stored. If more data is to be stored, control jumps back to step  420 ; otherwise, control jumps back to step  412  where the process waits for another request. 
       FIG. 5  is a flowchart outlining an exemplary data retrieval/read procedure for the RAID system according to the present disclosure. The process starts in step  502  where a RAID system is started and the disks synchronized. Then, in step  510 , a determination is made as to whether a request has been made to read data from the RAID. If a read request has been made, control continues to step  520 ; otherwise, control jumps to step  512  where the process waits for a next requests (read, write or otherwise) and a subsequent write determination in step  510  is made. 
     In step  520 , the location and size of the data to be retrieved is received. Next, in step  522 , the block information, i.e., where the data is stored, and the sector information, i.e., which sectors contain target data and which contain parity data, is determined. Then, in step  524 , an appropriate sector stripe can be read from the RAID systems&#39; disks. Control continues to step  526 . 
     In step  526 , a parity check can be performed on the read sector stripe, and the results can be optionally forwarded to any device that might make use of the information. Next, in step  528 , the target data can be extracted from the read sector stripe and forwarded to the intended recipient. Control continues to step  540 . 
     In step  540 , a determination is made as to whether there is more data to be retrieved. If more data is to be retrieved, control jumps back to step  522 ; otherwise, control jumps back to step  512  where the process waits for another request. 
       FIG. 6  is a flowchart outlining an exemplary degraded mode data retrieval and rebuilding procedure according to the present disclosure, which assumes that a disk has failed and/or a replacement disk has been supplied. As shown in  FIG. 6 , the procedure is very similar to that of  FIG. 5  with the exception of steps  626  and  628  replacing steps  526  and  528 . In step  626 , data from a failed disk is reconstructed using the remaining operational disks, assuming that the failed disk would not be supplying parity data. If the failed disk is known to carry a parity sector for the current sector stripe, then no data reconstruction may be necessary. The target data can then be forwarded to its intended destination. 
     In step  628 , parity data can be reconstructed, if necessary or desired, and the sector of lost target or parity data can be written to the replacement disk. 
     In various embodiments where the above-described systems and/or methods are implemented using a programmable device, such as a computer-based system or programmable logic, it should be appreciated that the above-described systems and methods can be implemented using any of various known or later developed programming languages, such as “C”, “C++”, “FORTRAN”, Pascal”, “VHDL” and the like. 
     Accordingly, various storage media, such as magnetic computer disks, optical disks, electronic memories and the like, can be prepared that can contain information that can direct a device, such as a computer, to implement the above-described systems and/or methods. Once an appropriate device has access to the information and programs contained on the storage media, the storage media can provide the information and programs to the device, thus enabling the device to perform the above-described systems and/or methods. 
     For example, if a computer disk containing appropriate materials, such as a source file, an object file, an executable file or the like, were provided to a computer, the computer could receive the information, appropriately configure itself and perform the functions of the various systems and methods outlined in the diagrams and flowcharts above to implement the various functions. That is, the computer could receive various portions of information from the disk relating to different elements of the above-described systems and/or methods, implement the individual systems and/or methods and coordinate the functions of the individual systems and/or methods described above. 
     The many features and advantages of the invention are apparent from the detailed specification, and thus, it is intended by the appended claims to cover all such features and advantages of the invention which fall within the true spirit and scope of the invention. Further, since numerous modifications and variations will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.