Abstract:
A data storage system includes a data management system that transfers data between a host system and multiple storage devices through multiple channels. The data addressing is distributed amongst channels to improve system performance and durability. In one embodiment, each channel has an address translation table or address map which is utilized to gain performance improvement during data transfer or erasure, and an increase of the device&#39;s useful life span.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims benefit of U.S. provisional patent application No. 60/854,940 filed Oct. 27, 2006 and entitled “Parallel Data Transfer and Structure,” which is incorporated herein by reference, and further, the present invention is related to co-pending U.S. patent application entitled “Multi-Channel Solid-State Storage System” filed on even date herewith, and co-pending U.S. patent application entitled “Parallel Data Transfer in Solid-State Storage” filed on even date herewith, each of which is incorporated herein by reference in its entirety. 
     
    
     BACKGROUND 
       [0002]    1. Field of Invention 
         [0003]    The present invention generally relates to data storage systems, and more particularly to data storage systems using one or more or solid-state storage devices. 
         [0004]    2. Description of Related Art 
         [0005]    The demand for solid-state data storage capacity, including Flash data storage capacity, is continually increasing. While the capacities available from storage devices are also increasing, many applications have data storage requirements that exceed the capacity available from a single storage device. One storage solution for these applications is a data storage system using more than one, or an array of, storage devices. 
         [0006]    Storage device arrays increase storage capacity by providing more storage locations to store data from a host system or host device. However, a host system typically transfers data to and from the data storage system at a faster rate than individual storage devices can read or write the data. Thus, while storage capacity may be increased by adding storage devices, the data transfer performance of the data storage system may not be improved, and thus, as a whole is typically limited to the level of performance of the individual storage devices. 
         [0007]    In light of the above, a need exists for improving the performance and the data transfer rate of a data storage system. 
       SUMMARY 
       [0008]    In various embodiments, a data storage system includes a data management system that transfers data between a host system and multiple storage devices. The transferred data includes data segments, each of which includes one or more data sectors. The data management system transfers the data segments to the storage devices in parallel through data channels. Additionally, the data management system updates a selected data sector contained in a storage device by performing an erasure operation on the selected data sector and writing an updated data sector into that storage device. In this way, the erasure operation is performed only in the storage device containing the selected data sector, which reduces the number of erasure operations in the storage devices that would otherwise occur if the data sectors of each data segment were distributed among the storage devices. 
         [0009]    The present invention improves the performance of conventional data storage systems by transferring data segments in parallel between the host system and the storage devices and by reducing the number of erasure operations performed to update data sectors in those data segments. The improvement in parallelism allows the array of storage devices to collectively attain a data transfer rate greater than that available from any of the storage devices individually. Further, the improvement in updating the data sectors reduces the number of erasure operations performed on the storage devices, which increases the lifetimes of the storage devices and the data storage system. 
         [0010]    A method for storing data, in accordance with one embodiment, includes receiving a plurality of data segments. Each data segment of the plurality of data segments includes at least one data sector. The method also includes storing the data segments in a buffer and distributing the data segments among a plurality of storage devices. The data segments are distributed among the plurality of storage devices such that the data segments are transferred to the plurality of storage devices substantially in parallel but the data sectors of each data segment are sequentially transferred to the storage devices. 
         [0011]    A method for storing data, in accordance with one embodiment, includes receiving a plurality of the data segments from a plurality of storage devices. Each data segment includes at least one data sector. The data segments are received substantially in parallel but the data sectors of each data segment are sequentially received from the storage devices. The method also includes storing the data segments into a buffer. 
         [0012]    A data storage system, in accordance with one embodiment, includes a plurality of storage devices, a plurality of communication channels corresponding to the plurality of storage devices, and a data management system coupled to the storage devices through the corresponding data channels. The data management system is configured to receive a plurality of data segments, each which at least one data sector. The data management system is further configured to distribute the data segments among the storage devices. The data management system distributes the data segments among the storage devices such that the data segments are transferred to the storage devices substantially in parallel but the data sectors of each data segment are sequentially transferred to the storage devices. 
         [0013]    A data storage system, in accordance with one embodiment, includes a plurality of storage devices and a data management system coupled to the storage devices. The data management system is configured to receive a plurality of the data segments from the storage devices. Each data segment includes at least one data sector. The data management system receives the data segments in parallel from the storage devices but receives the data sectors of each data segment sequentially from the storage devices. 
         [0014]    A method for storing data, in accordance with one embodiment, includes receiving a plurality of data segments. Each data segment of the plurality of data segments includes at least one data sector. The method further includes storing the plurality of data segments in a buffer and generating an address map for mapping each data segment of the plurality of data segments to a respective storage device of a plurality of storage devices. Additionally, the method includes distributing the data segments among the plurality of storage devices based on the address map, such that the data sectors of each data segment of the plurality of data sectors are sequentially transferred to the plurality of storage devices, and the data segments of the plurality of data segments are transferred to the plurality of storage devices substantially in parallel. 
         [0015]    A data storage system, in accordance with one embodiment, includes a plurality of storage devices, a plurality of communication channels corresponding to the plurality of storage devices, and a data management system coupled to the plurality of storage devices through the corresponding data channels. The data management system is configured to receive a plurality of data segments. Each data segment of the plurality of data segments includes at least one data sector. The data management system is further configured to generate an address map for mapping each data segment of the plurality of data segments to a respective storage device of the plurality of storage devices. Additionally, the data management system is further configured to distribute the data segments of the plurality of data segments among the plurality of storage devices based on the address map, such that the data sectors of each data segment of the plurality of data segments are sequentially transferred to a storage device of the plurality of storage device associated with the data segment, and the plurality of data segments are transferred to the plurality of storage devices substantially in parallel. 
         [0016]    The foregoing summary of embodiments of the present invention has been provided so that the nature of the present invention can be quickly understood. A more detailed and complete understanding of embodiments of the present invention can be obtained by reference to the following detailed description of the present invention together with the associated drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The accompanying drawings are included to provide a further understanding of the present invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the present invention, and together with the description, serve to explain the principles of the present invention. In the drawings, 
           [0018]      FIG. 1  is a block diagram of a data storage system coupled to a host system, in accordance with an embodiment of the present invention; 
           [0019]      FIG. 2  is a block diagram of a data management system, in accordance with an embodiment of the present invention; 
           [0020]      FIG. 3  is a block diagram of a buffer manager, in accordance with an embodiment of the present invention; 
           [0021]      FIG. 4  is a block diagram of an address map, or an address translation table, in accordance with an embodiment of the present invention; 
           [0022]      FIG. 5  is a block diagram of data segments striped across the storage devices, in accordance with an embodiment of the present invention; 
           [0023]      FIG. 6  is a block diagram of address maps, in accordance with an embodiment of the present invention; 
           [0024]      FIG. 7  is a block diagram of pages containing data sectors, in accordance with an embodiment of the present invention; 
           [0025]      FIG. 8  is a block diagram of storage devices containing data sectors, in accordance with an embodiment of the present invention; 
           [0026]      FIG. 9  is a flowchart of a method of transferring data in a data storage system, in accordance with an embodiment of the present invention; 
           [0027]      FIG. 10  is a flowchart of a portion of a method of transferring data in the data storage system, in accordance with an embodiment of the present invention; 
           [0028]      FIG. 11  is a flowchart of a portion of a method of transferring data in the data storage system in which data is written to data storage devices, in accordance with an embodiment of the present invention; 
           [0029]      FIG. 12  is a diagram representing a data transfer from a host system to storage devices in which data is written into the storage devices, in accordance with an embodiment of the present invention; 
           [0030]      FIG. 13  is a flowchart for a portion of a method of transferring data in the data storage system in which data is read from storage devices, in accordance with an embodiment of the present invention; and 
           [0031]      FIG. 14  is a diagram representing a data transfer in a data storage system in which data is transferred from storage devices to a host system, in accordance with an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0032]    In various embodiments, a data storage system includes a data management system and storage devices. The data management system communicates, and transfers data to and from, the storage devices through communication channels. The storage devices are coupled to the data management system through the channel corresponding to the storage device. In some embodiments, more than one storage devices may transfer data through one channel, while in other embodiments, there is a one-to-one correspondence between the number of channels and storage devices. 
         [0033]    The data management system receives data sequentially from a host system and transfers the data, as data segments, to the channels in parallel. Thus, the storage devices receive the data segments in a parallel manner. Additionally, the data management system receives data segments from the storage devices and channels in parallel. The data management system may reassemble the data segments into data for transfer to the host system, and sequentially transfers the data to the host system. 
         [0034]      FIG. 1  illustrates a data storage system  100 , in accordance with an embodiment of the present invention. The data storage system  100  includes a data management system  110  and storage devices  115  (e.g., storage devices  115   a ,  115   b ,  115   c , and  115   d ). The data management system  110  is coupled to the storage devices  115  through corresponding data channels  112  (e.g., data channels  112   a ,  112   b ,  112   c , and  112   d ). The data channels  112  may be referred to as channels or communication channels. The data channels  112  may be any system, device, connection, or interface system for facilitating communications between the data management system  110  and the storage devices  115 . For example, each of the communication channels  112  may a communication bus. Additionally, the data management system  110  is coupled to a host system  105 . As is described in more detail below, the data management system  110  stores data received from the host system  105  in the storage devices  115 . Additionally, the data management system  110  retrieves data stored in the storage devices  115  at the request of the host system  105  and transfers the requested data to the host system  105 . 
         [0035]    In one embodiment, the data storage system  100  includes four storage devices  115   a - d  coupled to the data management system  110  through four corresponding data channels  112   a - d . It is to be understood, however, that the present invention is not limited to four storage devices  115  or four data channels  112  and may be implemented with more or less than four storage devices  115  and more or less than four data channels  112 . For example, the data storage system  100  may include four, eight, sixteen, thirty-two, or any other number of storage devices  115  and data channels  112 . In some embodiments, there may be a one-to-one correspondence between the data channels  112  and storage devices  115 , and yet in other embodiments, there may not be a one-to-one correspondence. For example, in some embodiments, more than one storage device  115  may be coupled, and transferred data through, one data channel  112 . Although  FIG. 1  illustrates the data management system  110  and the storage devices  115   a - d  as separate components in the data storage system  100 , the data management system  110  and the storage devices  115   a - d  may be assembled and packaged as a single component or as separate components which are later connected together by an end user or manufacturer of the data storage system  100 . For example, the data management system  110  and the storage devices  115  may all be manufactured on an integrated circuit. 
         [0036]    In various embodiments, each of the storage devices  115  includes a storage medium for storing data. In operation, the storage devices  115  write data to the storage mediums and read data from the storage mediums. The storage medium of a storage device  115  may be any type of data storage, such as a flash storage system, a solid-state drive, a flash memory card, a secure digital (SD) card, a universal serial bus (USB) memory device, a CompactFlash card, a SmartMedia device, a flash storage array, or the like. One skilled in the art will recognize that other types of storage devices such as hard drives and optical media drives may also be used without departing from the scope of the present invention. The storage devices  115  may be the same type of device or may be different types of devices. The storage devices  115  may have the same storage capacity or the storage devices  115  may have differing storage capacities. 
         [0037]    The host system  105  may be any system or device having a need for data storage or retrieval and a compatible interface for communicating with the data storage system  100 . For example, the host system  105  may a computing device, a personal computer, a portable computer, or workstation, a server, a personal digital assistant, a digital camera, a digital phone, or the like. The host system  105  may communicate with the data storage system  100  by using a communication interface, such as an Integrated Drive Electronics (IDE) interface, a Universal Serial Bus (USB) interface, a Serial Peripheral (SP) interface, an Advanced Technology Attachment (ATA) interface, a Serial Advanced Technology Attachment (SATA), a flash interface, a Small Computer System Interface (SCSI), an IEEE 1394 (Firewire) interface, or the like. In some embodiments, the host system  105  includes the data storage system  100 . In other embodiments, the data storage system  100  is remote with respect to the host system  105  or is contained in a remote computing system coupled in communication with the host system  105 . For example, the host system  105  may communicate with the data storage system  100  via a wireless communication link. 
         [0038]      FIG. 2  illustrates components of the data management system  110 , in accordance with an embodiment of the present invention. The data management system  110  includes a controller  200 , a buffer manager  205 , a host interface  210 , a switch  215 , and storage interfaces  220  (e.g., storage interfaces  220   a ,  220   b ,  220   c , and  220   d ). The host interface  210  is coupled to the host system  105 , the controller  200 , and the switch  215 . The storage interfaces  220  are coupled to the controller  200  and the switch  215 . The storage interfaces  220  are also coupled to respective storage devices  115 . In this way, each storage interface  220  is associated with one of the storage devices  115 . In some embodiments, the storage interfaces  220  include buffers for synchronizing a data transfer rate of the switch  215  with a data transfer rate of the storage devices  115 . For example, each of the storage interfaces  220  may include a ping-pong buffer for synchronizing the data rate of the switch  215  with the data rate of the storage device  115  coupled to the storage interface  220 . The buffer manager  205  is coupled to the controller  200  and the switch  215 . Additionally, the controller  200  is coupled to the switch  215 . 
         [0039]    The host interface  210  facilitates communication between the host system  105  and the data management system  110 . The storage interfaces  220  facilitate communication between the data management system  110  and the storage devices  115 . The switch  215  functions to selectively connect the host interface  210  and storage interfaces  220  to the buffer manager  205 , thereby allowing the host interface  210  and the storage interfaces  220  to transfer data to and from the buffer manager  205 . The controller  200  monitors and controls operation of the data management system  110  and components contained therein. 
         [0040]    As mentioned above, the host interface  210  facilitates communication between the host system  105  and the data management system  110 . This communication includes the transfer of data as well as command and control information. In some embodiments, the host interface  210  is optional in the data management system  110 . For example, the host system  105  may include the host interface  210  or the host interface  210  may be between the host system  105  and the data management system  110 . In other embodiments, the host interface  210  is partially external of the data management system  110 . In one embodiment, the host interface  210  is an Advanced Technology Attachment (ATA) interface which functions as an ATA target device that receives and responds to commands from an ATA host operating in the host system  105 . In other embodiments, the host interface  210  may include another type of interface, which may use a variable or fixed data packet size. For example, the host interface  210  may include a Small Computer System Interface (SCSI), which uses a fixed data packet size. The host interface  210  may include a physical interface, such as CompactFlash or other ATA compatible interfaces. In some embodiments, a bridge or other conversion device may be used to interconnect the host interface  210  and the host system  105  through other types of ports or interfaces, such as a Universal Serial Bus (USB) port, a Serial Advanced Technology Attachment (SATA), a flash interface, or an IEEE 1394 (Firewire) port. 
         [0041]    The storage interfaces  220  facilitate communication between the data management system  110  and the storage devices  115 . This communication includes the transfer of data as well as command and control information in some embodiments. In one embodiment, the storage interfaces  220  are ATA interfaces implemented as ATA host devices and the storage devices  115  are implemented as ATA target devices. In this embodiment, the storage interfaces  220  generate commands which are executed by the storage devices  115 . The storage interfaces  220  are not limited to any one ATA interface standard and may use other types of interfaces, which may use a fixed or variable data packet size. For example, the storage interfaces  220  may include a SCSI interface, which uses a fixed data packet size. The storage interfaces  220  may include a physical interface such as a CompactFlash interface or other ATA compatible interfaces. Additionally, a bridge or other conversion device may be used to interconnect the storage interfaces  220  and the storage devices  115  through other types of ports, such as a USB port or an IEEE 1394 port. In some embodiments, the storage interfaces  220  may use a different type of interface than that used by host interface  210 . In some embodiments, the storage interfaces  220  may include a combination of interfaces. For example, some of the storage interfaces  220  may be CompactFlash interfaces and some of the storage interfaces  220  may be SCSI interfaces. The storage interfaces  220  may also use other interfaces such as SATA, a flash interface, or the like 
         [0042]    In one embodiment, the switch  215  is a multiple port bus. In this embodiment, the host interface  210 , each of the storage interfaces  220 , and the buffer manager  205  are coupled to a respective port of the multiple port bus. The controller  200  controls the operation of the switch  215  to selectively connect the host interface  210  and the storage interfaces  220  to the buffer manager  205 . Additional details on the connections between the host interface  210 , the storage interfaces  220 , and the buffer manager  205  according to one embodiment are provided below. Not all embodiments will have all the components or connections depicted in  FIG. 2 , and some embodiments may have additional components or connections not depicted in  FIG. 2 . 
         [0043]      FIG. 3  illustrates the buffer manager  205 , in accordance with an embodiment of the present invention. The buffer manager  205  includes a read arbiter  300 , a write arbiter  305 , and a buffer memory  310  (e.g. a buffer). The buffer memory  310  is used to store data being transferred between the host system  105  and the storage devices  115 . The buffer memory  310  may include any type of buffer, register, memory, or storage, such as a random access memory (RAM), a dynamic random access memory (DRAM), a static random access memory (SRAM), a synchronous dynamic random access memory (SDRAM), a flash storage, an erasable programmable read-only-memory (EPROM), an electrically erasable programmable read-only-memory (EEPROM), or the like. The buffer memory  310  may be a single port memory or a dual port memory or the like. 
         [0044]    The buffer memory  310  preferably includes sufficient storage capacity to store a maximum amount of data to be transferred between the host system  105  and the storage devices  115  during a single read or write operation. For example, under an ATA standard, 256 sectors of 512 bytes each is the maximum amount of data read or written in response to a single ATA command. In this example, buffer memory  310  has sufficient capacity to store at least 256 sectors of data (e.g., 256 data sectors). 
         [0045]    The read arbiter  300  and the write arbiter  305  handle requests for operations on the buffer memory  310 . Specifically, the read arbiter  300  manages requests for read operations for transferring data from the buffer memory  310 , and the write arbiter  305  manages requests for write operations for transferring data to the buffer memory  310 . In one embodiment, each of the read arbiter  300  and the write arbiter  305  is implemented using digital logic and is capable of managing three simultaneous requests received from any of the controller  200 , the host interface  210 , or the storage interfaces  220 . The read arbiter  300  and the write arbiter  305  may handle more or fewer than three simultaneous requests in other embodiments. 
         [0046]    Priorities for granting access to buffer memory  310  may be varied depending on the design requirements of the data storage system  100 . For example, requests from the controller  200  may be given top priority followed by requests from the host interface  210  and the storage interfaces  220 . One skilled in the art will recognize that arbiters having different configurations and capacities may be used in various embodiments of the present invention. 
         [0047]    The controller  200  may include a microprocessor, a microcontroller, an embedded controller, a logic circuit, software, firmware, or any kind of processing device. In one embodiment, the controller  200  is a microcontroller including a processor and a memory, which is programmed to execute code for performing the operations of the data storage system  100 . In other embodiments, controller  200  may include a microprocessor and a finite state machine, or may include a call processor. Although only a single controller  200  is illustrated in  FIG. 2 , it is to be understood that the data management system  110  may include more than one controller  200  with various control tasks being distributed between the controllers  200 . The operation of the controller  200  will be described further below. 
         [0048]    Some or all of the components of the data management system  110  described above may be implemented using individually packaged application specific integrated circuits (ASICs) or programmable gate arrays. For example, the host interface  210 , the storage interfaces  220 , the switch  215 , and the buffer manager  205  may be implemented using a single ASIC or a single field programmable gate array (FPGA). 
         [0049]    The data storage system  100  further includes address maps  315  corresponding to the data channels  112  and storage devices  115  for mapping addresses of the host system  105  to addresses of the storage devices  115 . The address maps  315  may also be referred to as address translation table, logical-to-physical table, virtual-to-physical table, directory, or the like. The address maps  315  may be any type of data structure, such as a table. For example, an address map  315  may be a logical-to-physical address table, a virtual-to-physical address table, a translation table, a directory, a formula, or the like. In one embodiment, each of the address maps  315  maps logical block addresses (LBAs) of the host system  105  to physical block addresses (PBAs) of the storage device  115  corresponding to the address map  315 . In various embodiments, an LBA of the host system  105  identifies data to be transferred between the host system  105  and one or more of the storage devices  115 . A data segment is a portion of data which may comprise a data sector, two or more data sectors, or a portion of a data sector, depending on the embodiment or implementation. The address map  315  maps each data segment identified by the LBA to a PBA of one of the storage devices  115 . 
         [0050]    In some embodiments, the address map  315  maps the data identified by an LBA of the host system  105  to respective PBAs across the storage devices  115  such that the data is striped across the storage devices  115 . In these embodiments, each of the address maps  315  maps a data block identified by an LBA of the host system  105  to a respective PBA in the storage device  115  corresponding to the address map. In this way, the each data sector in a data segment is mapped to the same storage device  115 . An advantage of mapping the data sectors of a data segment to the same storage device  115  is that an erasure operation need only be performed on that storage device  115  when a data sector in the data segment is updated in a write operation. Consequently, the number of overall erasure operations performed on the storage devices  115  is reduced, which increases the lifetimes of the storage devices  115  and the data storage system  100 . 
         [0051]    In one embodiment, data segments are mapped to corresponding data channels  112  and storage devices  115  based on least significant bits of the LBAs of the data segments. For example, a data segment may be mapped to a data channel  112  computing a value equal to the LBA modulo the number of data channels  112  in the data storage system  100 . In one embodiment, the data storage system  100  includes four data channels  112 . In this embodiment, LBAs having two least significant bits equal to ′b00 are mapped to a first data channel  112  (e.g., data channel  112   a ), LBAs having two least significant bits equal to ′b01 are mapped to a second data channel  112  (e.g., data channel  112   b ), LBAs having two least significant bits equal to ′b10 are mapped to a third data channel  112  (e.g., data channel  112   c ), and LBAs having two least significant bits equal to ′b11 are mapped to a fourth data channel  112  (e.g., data channel  112   d ). Moreover, the data storage system  100  transfers data segments between the data management system  110  and the storage devices  115  through the data channels  112  corresponding to the LBAs of the data segments. In other embodiments, the data storage system  100  may have more or fewer than four data channels  112 , such as 2, 8, 16, 32, or any other number of channels which may not necessarily be a power of 2 in the particular embodiment. 
         [0052]    Although  FIG. 3  illustrates the address maps  315  in the buffer memory  310 , the address maps  315  may be external of the buffer memory  310  or external of the buffer manager  205  in other embodiments. In some embodiments, the address maps  315  are stored in a random access memory of the data storage system  100 . For example, the random access memory may be a static random access memory (SRAM) or a dynamic random access memory (DRAM). 
         [0053]    In some embodiments, the data management system  110  includes a flash storage for storing the address maps  315 . In these embodiments, the data management system  110  loads the address maps  315  from the flash storage into the random access memory at the occurrence of an event, such as power-up or reset of the data management system  110 . Further, the data management system  110  stores the address maps  315  into the flash storage at the occurrence of an event, such as power-down of the data management system  110 , or during power failure. In this way, the address maps  315  are maintained in the flash storage during power-down or reset of the data management system  110 . 
         [0054]      FIG. 4  is a block diagram of the address map  315 , in accordance with an embodiment of the present invention. The address map  315  includes logical block addresses (LBAs)  400  of the host system  105  and physical block address (PBAs)  405  of the storage device  115  corresponding to the address map  315 . In this embodiment, the address map  315  maps data segments identified by an LBA  400  of the host system  105  to respective PBAs  405  the storage device  115  corresponding to the address map  315 . 
         [0055]      FIG. 5  is a block diagram of data segments  500  striped across the storage devices  115 , in accordance with an embodiment of the present invention. In this embodiment, the data management system  110  receives the data segments  500   a - h  sequentially from the host system  105  and maps the LBAs  400  data segments  500   a - h  to PBAs  405  of the storage devices  115   a - d  such that the data segments  500   a - h  are striped across the storage devices  115   a - d . As illustrated in  FIG. 5 , the storage device  115   a  contains the data segments  500   a  and  500   e , the storage device  115   b  contains the data segments  500   b  and  500   f , the storage device  115   c  contains the data segments  500   c  and  500   g , and the storage device  115   d  contains the data segments  500   d  and  500   h.    
         [0056]      FIG. 6  is a block diagram of the address maps  315 , in accordance with an embodiment of the present invention. In this embodiment, the address maps  315   a - d  map LBAs  400   a - h  of the data segments  500   a - h  to PBAs  405   a - h  of the storage devices  115   a - d  such that the data segments  500   a - h  are striped across the storage devices  115   a - d . The address map  315   a  maps the LBA  400   a  of the data segment  500   a  to the PBA  405   a  of the storage device  115   a  and the LBA  400   e  of the data segment  500   e  to the PBA  405   e  of the storage device  115   a . The address map  315   b  maps the LBA  400   b  of the data segment  500   b  to the PBA  405   b  of the storage device  115   b  and the LBA  400   f  of the data segment  500   f  to the PBA  405   f  of the storage device  115   b . The address map  315   c  maps the LBA  400   c  of the data segment  500   c  to the PBA  405   c  of the storage device  115   c  and the LBA  400   g  of the data segment  500   g  to the PBA  405   g  of the storage device  115   c . The address map  315   d  maps the LBA  400   d  of the data segment  500   d  to the PBA  405   d  of the storage device  115   d  and the LBA  400   h  of the data segment  500   h  to the PBA  405   h  of the storage device  115   d . The mappings are used as an illustrative example to describe the invention since in many data transfers, or many storage systems, there are substantially more mappings referencing a larger storage area than depicted in these examples. 
         [0057]    In a further embodiment, the LBAs  400  of the address maps  315  are mapped to the storage devices  115  based on the least significant bits of the LBAs  400 . For example, the least significant bits of the LBAs  400  in the address map  315   a  of the storage device  115   a  may be equal to b′ 00 , the least significant bits of the LBAs  400  in the address map  315   b  of the storage device  115   b  may be equal to b′01, the least significant bits of the LBAs  400  in the address map  315   c  of the storage device  115   c  may be equal to b′10, and the least significant bits of the LBAs  400  in the address map  315   d  of the storage device  115   d  may be equal to b′  11 . In this way, consecutive LBAs  400  are striped across the storage devices  115  based on the address maps  315  containing the LBAs  400 . 
         [0058]      FIG. 7  illustrates data segments  500   a - d  containing data sectors  505 , in accordance with an embodiment of the present invention. In this example, the data segment is a page of data as conventionally known in the art. As illustrated, each of the data segments  500  includes four data sectors  505 . Data segment  500   a  includes the sequence of data sectors  505   a  (Sector  0 ),  505   b  (Sector  1 ),  505   c  (Sector  2 ), and  505   d  (Sector  3 ). Data segment  500   b  includes the sequence of data sectors  505   e  (Sector  4 ),  505   f  (Sector  5 ),  505   g  (Sector  6 ), and  505   h  (Sector  7 ). Data segment  500   c  includes the sequence of data sectors  505   i  (Sector  8 ),  505   j  (Sector  9 ),  505   k  (Sector  10 ), and  505   l  (Sector  11 ). Data segment  500   d  includes the sequence of data sectors  505   m  (Sector  12 ),  505   n  (Sector  13 ),  505   o  (Sector  14 ), and  505   p  (Sector  15 ). In a write operation, the data segments  500   a - d  are transferred from the host system  105  to the storage devices  115  according to the address map  315 . In this process, the data management system  110  associates a PBA  405  with each data sector of a data segment  500   a - d  based on the LBA  400  of the data segment. In one embodiment, the first data sector  505  (e.g., sector  505   a ) in a data segment  500  (e.g., data segment  500   a ) is mapped to a PBA  405  of a storage device  115  and each subsequent data sector (e.g., sectors  505   c - d ) in the sequence of data sectors in the data segment  500  (e.g., data segment  500   a ) is mapped to an offset of the PBA  405 . For example, the least significant bits of the PBA for the first data sector may be equal to b′00, the least significant bits of the PBA for the second data sector may be equal to b′01, the least significant bits of the PBA for the third data sector may be equal to b′ 10, and the least significant bits of the PBA for the fourth data sector may be equal to b′ 11. The data management system  110  then transfers each data sector to the storage device  115  based on the PBA  405  associated with the data sector. 
         [0059]      FIG. 8  illustrates the storage devices  115  containing data sectors, in accordance with an embodiment of the present invention. As may be envisioned from  FIG. 7 , each of the data segments  500 , or pages, is stored in a corresponding storage device  115   a - d  such that the data sectors  705  of a given data segment  500  are stored in the same storage device  115  according to the address map  315  of  FIG. 5 . As illustrated in  FIG. 8 , the storage device  115   a  contains the data sectors  705   a  (Sector  0 ),  705   b  (Sector  1 ),  705   c  (Sector  2 ), and  705   d  (Sector  3 ). The storage device  115   b  contains the data sectors  705   e  (Sector  4 ),  705   f  (Sector  5 ),  705   g  (Sector  6 ), and  705   h  (Sector  7 ). The storage device  115   c  contains the data sectors  705   i  (Sector  8 ),  705   j  (Sector  9 ),  705   k  (Sector  10 ), and  705   l  (Sector  11 ). The storage device  115   d  contains the data sectors  705   m  (Sector  12 ),  705   n  (Sector  13 ),  705   o  (Sector  14 ), and  705   p  (Sector  15 ). 
         [0060]    While  FIGS. 7 and 8  illustrate a data segment comprising a page (e.g. conventionally  4  sectors), other embodiments may utilize a data segment more or less section (e.g. 1, 2, or more sectors), or a portion of a sector. 
         [0061]      FIG. 9  illustrates a method of transferring data in the data storage system  100 , in accordance with an embodiment of the present invention. The method represents the general operating process executed by the data storage system  100 . The process may be initiated at power up, following a reset of the data storage system  100 , or at another time as desired. 
         [0062]    In step  900 , the controller  200  runs a diagnostic test in one or more of the storage devices  115 . The diagnostic test confirms operability and determines the current status of the storage devices  115 . The type of diagnostic test may depend upon the type of the storage device  115  and are well known to those skilled in the art. During execution of the diagnostic tests, the host interface  210  preferably provides a busy indicator to the host system  105  indicating that the data storage system  100  is currently unavailable. The method then proceeds to step  905 . 
         [0063]    In step  905 , the controller  200  receives results of the diagnostic tests from the storage devices  115 . If a result received from any of the storage devices  115  indicates an error has occurred in the storage device  115 , the method proceeds to step  910 . Otherwise each storage device  115  provides a ready indicator to the controller  200 , and the controller  200  sends a ready indicator to the host system  105  via the host interface  210 . For example, the controller  200  may send a ready indicator to the host system  105  indicating the status (e.g., ready) of the data management system  110 . The method then proceeds to step  915 . 
         [0064]    In step  910 , arrived at from the determination in step  905  that an error has occurred in the storage devices  115 , the controller  200  determines the type of error that has occurred and stores data representing the error, for example in an error register. The controller  200  then reports the error to host system  105  via host interface  210 . For example, the controller  200  may provide an error indicator to the host system  105  via the host interface  210 . If the controller  200  reports the error to host system  105 , the data management system  110  may perform additional operations in various embodiments. In one embodiment, the host system  105  provides a reset command to the controller  200  to attempt to clear any errors by resetting the data storage system  100 . If the error persists, or if the type of error reported to host system  105  is not likely to be cleared through a reset, the host system  105  may notify a user of the error and shut down data storage operations until the data storage system  100  is fully operational. Alternatively, if one or more of the storage devices  115  provides a ready indicator to the data management system  110  after the data storage system  100  is reset, the controller  200  reports a ready indicator to the host system  105 . The method then proceeds to step  915 . 
         [0065]    In step  915 , arrived at from the determination in step  905  that an error has not occurred in one of the storage devices or from step  910  in which an error status has been reported to the host system  105 , the data management system  110  waits to receive a command from the host system  105 . If the data management system  110  receives a command from the host system  105 , the host interface  210  stores the command in one or more command registers and notifies the controller  200  that a command has been received. The method then proceeds to step  920 . 
         [0066]    In step  920 , the controller  200  retrieves the command from the command registers, decodes the command, and executes the command. Possible commands include, but are not limited to, a fix data transfer command (e.g., identify drive), a write command, a read command, an erasure command, or a purge command. In response to any command either not recognized or simply not supported by the data storage system  100 , the controller  200  provides an abort command indicator to the host system  105  via the host interface  210 . 
         [0067]    For fix data transfer commands, the controller  200  issues requests for drive information to each of the storage devices  115  via the respective storage interfaces  220 . The request format and protocol may vary depending on the type of storage device  115  and are well known to those skilled in the art. The drive information is then reported to the host system  105  via the host interface  210 . Likewise, in response to a purge command, the controller  200  issues a purge command to each of the storage devices  115  via the respective storage interfaces  220 . The format and protocol of the purge command may vary depending on the type of the storage device  115  and are well known to those skilled in the art. The method then returns to step  1015 . In an alternative embodiment, the method ends instead of returning to step  915 . 
         [0068]      FIG. 10  illustrates a portion of a method of transferring data between the host system  105  and the storage devices  115 , in accordance with an embodiment of the present invention. This portion of the method is performed in response to the data management system  110  receiving a read command or a write command from the host system  105 . In various embodiments, this portion of the method is performed in step  920  of  FIG. 9 . In this portion of the method, the controller  200  determines that the command received from the host system  105  is a read command or a write command, calculates the parameters of the data transfer based on the command, initiates the system hardware to be used in the data transfer, and initiates the data transfer. Upon completion of the data transfer, the controller  200  confirms the data transfer and provides an error report or a completion report to the host system  105  via the host interface  210 . This portion of the method is described more fully below, in which various steps of the method are described in more detail. 
         [0069]    In step  1000 , the host interface  210  receives a command from the host system  105  and stores the command in one or more command registers. The controller  200  retrieves the command from the command registers and calculates parameters for the data transfer. The parameters of the data transfer include the logical block address (LBA) and the block count, or number of sectors, of the data to be transferred. Using these parameters, the controller  200  calculates parameters for one or more direct memory access (DMA) transfers for transferring the data between the storage devices  115  and the host system  105 . For example, each of the host interface  210  and the storage interfaces  220  may include a DMA engine used to transfer data between an internal buffer of the respective host interface  210  or storage interface  220  and the buffer manager  205 . The controller  200  provides each of these DMA engines with data transfer parameters which include addresses, a transfer count, and a transaction size. The method then proceeds to step  1005 . 
         [0070]    In step  1005 , the controller  200  initiates the hardware to be used in the data transfer. This includes providing the respective DMA engines with the transfer parameters mentioned above. In addition, the controller  200  sends commands to the storage devices  115  via the respective storage interfaces  220  to set up the data transfer. The method then proceeds to step  1010   
         [0071]    In step  1010 , the DMA engines of the storage interfaces  220  transfer the data to the respective storage devices  115 , and the storage devices  115  store the data. If a data error occurs in any of the storage devices  115 , the storage device  115  in which the data error occurs provides an error indicator to the controller  200  via the respective storage interface  220 . The method then proceeds to step  1015 . 
         [0072]    In step  1015 , the controller  200  determines whether an error has occurred in any of the storage devices  115  based on whether the controller  200  receives an error indicator from any of the storage devices  115  or if a time-out condition occurs in the data transfer. If the controller  200  determines an error has occurred in one or more of the storage devices  115 , this portion of the method proceeds to step  1120 . Otherwise the controller  200  sends a ready indicator to the host system  105  via the host interface  210  and this portion of the method proceeds to step  1125 . The method then proceeds to step  1020 . 
         [0073]    In step  1020 , arrived at from the determination in step  1115  that an error has occurred in the storage devices  115 , the controller  200  determines the type of error that has occurred and reports the error to host system  105  via the host interface  210 . For example, the controller  200  may provide an error indictor or send an error message to the host system  105 . Additionally, the controller  200  may store a representation of the error message, for example in an error register, for subsequent access by the host system  105 . The method then proceeds to step  1025 . 
         [0074]    In step  1025 , arrived at from the determination in step  1115  that an error has not occurred in any of the storage devices  115  or from step  1120  in which an error has been reported to the host system  105 , the controller  200  reports the completion of the data transfer to the host system  105 . This portion of the method then ends. In an alternative embodiment, this portion of the method instead returns to step  915  of  FIG. 9 . 
         [0075]      FIG. 11  illustrates a portion of a method of writing data to the storage devices  115   a - d , in accordance with an embodiment of the present invention. For example, this portion of the method of transferring data from the host system  105  to the storage devices  115  may be performed in response to the data management system  110  receiving a write command from the host system  105 . In various embodiments, this portion of the method is performed during step  1010  of  FIG. 10 . The data management system  110  receives data from the host system  105  and stores the data. The data management system  110  then distributes the data among the storage devices  115  and the storage devices  115  store the data. This portion of the method is described more fully below, in which various steps of the method are described in more detail. 
         [0076]    In step  1100 , the host interface  210  receives data from the host system  105 . The data of a data unit may be any portion of the data unit. As data is received, the host interface  210  facilitates the storage of the data segments in a buffer, which may be internal or external of the host interface  210 . The host interface  210  may also receives a write command from the host system  105  along with the data segments. The method then proceeds to step  1105 . 
         [0077]    In step  1105 , the DMA engine of the host interface  210  transfers the data to the buffer memory  310  of the buffer manager  205  based on the write command. If the buffer memory  310  is implemented using a dual port memory, the host interface  210  may be connected directly to one of the ports of the buffer memory  310  so that the DMA engine of the host interface  210  writes the data into the buffer memory  310  without going through switch  215 . Additionally, the controller  200  may be configured to directly access to the buffer manager  205  without having to go through the switch  215 . If the buffer memory  310  is implemented as a single port memory, the DMA engine of the host interface  210  transfers the data segments to buffer memory  310  via switch  215 . 
         [0078]    In the arrangement shown in  FIG. 2 , in which the host interface  210  is coupled to the buffer manager  205  via the switch  215 , access to the buffer manager  205  is granted using an arbitration scheme. Specifically, the switch  215  is controlled by the controller  200  to selectively couple the host interface  210  and the storage interfaces  220  to buffer manager  205  by alternating access to the buffer manager  205  from the host interface  210  and one of storage interfaces  220  based on an arbitration scheme. Possible arbitration schemes include, but are not limited to, a round-robin scheme, a fixed priority scheme, a dynamic priority scheme, and the like. For example, a fixed priority scheme may provide access from the host interface  210  to the buffer manager  205  and then successively provide access from each of the storage interfaces  220  to the buffer manger  205  in a predetermined order before again providing access from the host interface  210  to the buffer manager  205 . 
         [0079]    As another example, a dynamic priority scheme may provide access from the host interface  210  and the storage interfaces  220  to the buffer manager  205  based on measured performance characteristics of the data management system  110 . In the way, performance of the data management system  110  may be optimized based on the performance characteristics. The arbitration of access by the individual storage interfaces  220  is described in more detail below. During each time slot of the arbitration scheme, the DMA engine of the host interface  210  transfers a portion of the data to the buffer manager  205 . By alternating access to the buffer manager  205 , the subsequent transfer of data to the storage devices  115  may begin prior to receiving all of the data from the host system  105 . The method then proceeds to step  1110 . 
         [0080]    In step  1110 , the data stored in the buffer manager  205  is distributed among the storage devices  115 . In this process, data segments are individually transferred from the buffer manager  205  to one of the storage interfaces  220 . In this way, the data segments are distributed among the storage devices  115   a - d  coupled to the respective storage interfaces  220 . In one embodiment, each of the storage interfaces  220  includes a DMA engine that transfers the data segments from the buffer manager  205  to the corresponding storage interface  220  in a DMA transfer. 
         [0081]    In various embodiments, the data segments are transferred to the storage interfaces  220  using an arbitration scheme. In this process, a data segment is selected based on an arbitration scheme and are transferred to one storage interface  220  by the DMA engine of that storage interface  220  during sequential time slots. The next data segment is then selected and transferred to another storage interface  220  by the DMA engine of that storage interface  220  during sequential time slots. The arbitration scheme may include a round-robin scheme, a fixed priority scheme, a dynamic priority scheme, or any other arbitration scheme. Using the round-robin scheme for example, each of the storage interfaces  220  receives the data segments during each round of the arbitration scheme. For example, the storage interface  220   a  receives a first data segment, the storage interface  220   b  receives a second data segment, the storage interface  220   c  receives a third data segment, and the storage interface  220   d  receives a fourth data segment. The process is then repeated until all of the data segments are transferred from the host system  105  to the storage interfaces  220 . 
         [0082]    In one embodiment, the data segments are routed to particular storage interfaces  220  using a static routing algorithm controlled by the controller  200 . In this process, a given data segment is sent to the same storage interface  220  for storage in a respective storage device  115 . For example, all of the data of a first data segment are sent to the storage interface  220   a , all of the data of a second data segment are sent to the storage interface  220   b , all of the data of a third data segment are sent to the storage interface  220   c , and all of the data for a forth data segment are sent to the storage interface  220   d . This process is repeated to distribute the data segments among the storage interfaces  220   a - d.    
         [0083]    Access to the buffer manager  205  may be allocated between the host interface  210  and the storage interfaces  220  by using an arbitration scheme. In this way, the switch  215  is controlled to alternate access to the buffer manager  205  between the host interface  210  and the storage interfaces  220 . For example, using a round-robin scheme, the switch  215  is controlled to allow the host interface  210  to facilitate the transfer of one data segment to the buffer manager  205 , followed by the storage interface  220   a  transferring one data segment out of the buffer manager  205 , followed by the host interface  210  transferring another data segment to the buffer manager  205 , and then the storage interface  220   b  transferring a data segment out of buffer manager  205 . This allocation process is repeated to allow each of the storage interfaces  220  access to the buffer manager  205  with alternating access being granted to the host interface  210 . 
         [0084]    In various embodiments, the data segments are distributed among the storage interfaces  220  based on the write command. This distribution process may promptly begin as soon as data is available in the buffer manager  205 . Alternatively, the distribution process may wait until a minimum number of data segments have been transferred and stored in the buffer manager  205  before starting the distribution process. In one embodiment, the distribution process begins once the number of data segments stored in the buffer manager  205  is sufficient to allow the transfer of data to begin for one of the storage interfaces  220 . Splitting access to the buffer manager  205  between the host interface  210  and the storage interfaces  220  allows the distribution of data segments to occur while the transfer of data into the buffer manager  205  continues until all the data segments have been received from the host system  105 . 
         [0085]    During the data distribution process, the controller  200  monitors each of the buffers internal to the storage interfaces  220  to prevent overflow from occurring. In the event that one of the storage interfaces  220  has no capacity for receiving additional data, the controller  200  stops the transfer of data to that storage interface  220  until the buffer has recovered. During this time, data transfers from the host interface  210  into the buffer manager  205  may continue. In addition, the controller  200  uses a buffer register to monitor and control the flow of data into the buffer manager  205 . The buffer register includes one or more registers and a finite state machine. The buffer register is updated by the controller  200  to reflect the status of the buffer manager  205 . The status information in the buffer register may include a full/empty indicator, a capacity used indicator, a capacity remaining indicator, among others. The buffer register may be part of the controller  200  or the buffer manager  205 , or the buffer register may be implemented as a separate component accessible by the controller  200 . The method then proceeds to step  1115 . 
         [0086]    In step  1115 , the data segments received by the storage interfaces  220  are transferred to the respective storage devices  115 . In this process, the storage interfaces  220  may store the data segments before the data segments are transferred to the respective storage devices  115 . This data transfer process occurs in parallel thereby providing improvements to overall storage performance of the data storage system  100 . These advantages become significant when the data transfer rates of the individual storage interfaces  220  and the storage devices  115  are slower than the data transfer rate between the host system  105  and the host interface  210 . For example, solid-state storage devices using flash memory typically have a data transfer rate slower than that of conventional hard drives. In various embodiments, an array of solid-state storage devices may be used as the storage devices  115  to provide a cumulative data transfer rate comparable to that of a typical hard disk drive. The method then proceeds to step  1120 . 
         [0087]    In step  1120 , the storage devices  115  store the data received from the respective storage interfaces  220 . Improvements in the overall data transfer rate of the data storage system  100  are achieved when the individual components of the data storage system  100  have adequate data transfer rates. For example, in the above-described embodiment in which the switch  215  allocates access to the buffer manager  205  between the host interface  210  and the storage interfaces  220 , the switch  215  should have a data transfer rate at least twice as fast as the fastest data transfer rate of each of the storage interfaces  220 . This allows the data transfer through the data storage system  100  to be maintained without the back end data transfer to the storage devices  115  having to wait for data transfers on the front end from the host system  105 . 
         [0088]    In one embodiment, the host interface  210  receives a write command in step  1100  along with an updated data segment for updating a selected data segment in one of the storage devices  115 . In this embodiment, the host interface  210  transfers the updated data segment to the buffer memory  310  of the buffer manager  205  in step  1105  based on the write command. In step  1110 , the controller  200  identifies the storage device  115  containing the selected data segment and transfers the updated data segment to the storage interface  220  coupled to the storage device  115 . In turn, the storage interface  220  transfers the updated data segment into the storage device  115  containing the previous data segment for replacement of the previous data segment with the updated data segment. In this process, the controller  200  may provide an erasure command to the storage device  115  for erasing the previous data segment from the storage device  115  followed by a write command for writing the updated data segment into the storage device  115 . Because the data of the updated data segment are stored in the same storage device  115 , the erasure operation occurs only in that storage device  115 . In this way, the overall number of erasure operations performed on the storage devices  115  of the data storage system  100  is reduced. Because the lifetime of each storage device  115  is inversely related to the number of erasure operations performed on that storage device  115 , reducing the number of erasure operations performed on each storage device  115  increases the lifetimes of the storage devices  115  and the data storage system  100 . 
         [0089]    Once the data transfer is completed, this portion of the method ends. In one embodiment, the method then proceeds to step  1015  of  FIG. 10 , in which it is determined if an error occurred during the data transfer. If an error occurred in any of the storage devices  115  during the data transfer, the controller  200  reports the error to host system  105  in step  1020 . If no error occurred in any of the storage devices  115  during the data transfer, the controller  200  reports the completion of the data write command in step  1025 . 
         [0090]    An optimal number of data sectors in each data segment, and hence a preferred size of the individual data sectors, is influenced by several factors. For example, the internal data bus bandwidth of the switch  215  sets one performance limit. The internal data bus bandwidth (P) is the sum of the effective bandwidth (E), the overhead bandwidth (O), and the idle bandwidth (I) of the switch  215 . As data segment size is reduced, system overhead increases due to the increase in switching and in the number of data transfer transactions that are completed. As overhead increases, the effective bandwidth of the switch  215  decreases thereby reducing performance of the data storage system  100 . 
         [0091]    Another factor that influences the data segment size is the capacity of internal buffers of the host interface  210  and the storage interfaces  220 , which are typically implemented as first-in-first-out (FIFO) buffers. As the data segment size increases, the internal buffers store more data prior to transferring the data. Larger buffers require larger logic circuits in the host interface  210  and storage interfaces  220 , which may not be acceptable in view of other design constraints. 
         [0092]    Yet another factor is the back-end bandwidth available from the storage devices  115 . The back-end bandwidth is derived from a combination of the number of storage devices  115  used in the system and the individual bandwidths of the storage devices  115 . Once the effective bandwidth (E) of the switch  215  reaches the back end bandwidth of the storage devices  115 , increasing the data segment size may not result in additional significant performance improvements of the data storage system  100 . 
         [0093]      FIG. 12  illustrates a data transfer from the host system  105  to the storage devices  115   a - d , in which data is written into the storage devices  115   a - d , in accordance with an embodiment of the present invention. For example, the data transfer from the host system  105  to the storage devices  115   a - d  may be a write operation. In the data transfer, the data management system  110  receives a sequence  1200  of eight data segments  500  (e.g., data segments  500   a - h ) from the host system  105 . The eight data segments are used as for exemplary illustrative purposes to describe the invention; however, in many data transfers would involve substantially more data segments. The data management system  110  transfers a sequence of two data segments  1205  to the storage device  115   a , a sequence of two data segments  1210  to the storage device  115   b , a sequence of two data segment  1215  to the storage device  115   c , and a sequence of two data segments  1220  to the storage device  115   d . As illustrated in  FIG. 12 , each of the sequences of data segments  1205 ,  1210 ,  1215 , and  1220  are transferred to the storage devices  115   a - d  subsequent to the time slot in which the data segment  1202  is received by the data management system  110  from the host system  105  in the sequence of data segments  1200 . 
         [0094]    Because the data transfer rate from the host system  105  to the data management system  110  is generally faster than the data transfer rate from the data management system  110  to each of the individual storage devices  115 , the transfer of each sequence of data segments  1205 ,  1210 ,  1215 , and  1220  overlaps the transfer of at least one other sequence of data segments  1205 ,  1210 ,  1215 , or  1220  in time. Stated differently, the sequence of data segments  1205 ,  1210 ,  1215 , and  1220  are transferred from the data management system  110  to the storage devices  115  substantially in parallel. This is possible because each of the storage interfaces  220  independently transfers a respective sequence of data segments  1205 ,  1210 ,  1215 , and  1220  to the respective storage devices  115  through the corresponding data channels  112   a - d  after that storage interface  220  receives the first data segments  1202  of the sequence  1205 ,  1210 ,  1215 , or  1220  from the host interface  210 . 
         [0095]      FIG. 13  illustrates a portion of a method of transferring data from the storage devices  115  to the host system  105 , in accordance with an embodiment of the present invention. For example, this portion of the method of transferring data from the storage devices  115  to the host system  105  may be performed in response to the data management system  110  receiving a read command from the host system  105 . In various embodiments, this portion of the method is performed during step  920  of  FIG. 9 . The data management system  110  requests data segments (e.g., data segments  500   a - h ) from the storage devices  115 . The data segments are then transferred from the storage devices  115  to the respective storage interfaces  220 . The data segments are then transferred from the storage interfaces  220  to the buffer manager  205  using an arbitration scheme, such as a round-robin arbitration scheme. In this process, a data segment is selected based on the arbitration scheme and the data segments are transferred from the storage interface  220  containing the selected data segment to the buffer manager  205  during sequential time slots. The next data segment is then selected and transferred from the storage interface  220  containing this data segment to the buffer manager  205  during sequential time slots. The buffer manager  205  transfers the data segment to the host system  105  via the host interface  210 . This portion of the method is described more fully below, in which various steps of the method are described in more detail. 
         [0096]    In step  1300 , the data segments requested by host system  105  are received by the storage interfaces  220  from the respective storage devices  115 . In one embodiment, the controller  200  receives a read command from the host system  105  via the host interface  210  and provides a read command to each of the storage devices  115  via the respective storage interfaces  220 . Each of the storage interfaces  220  then individually transfers one or more data segments to the respective storage interface  220  based on the read command received from the respective storage interface  220 . The method then proceeds to step  1305 . 
         [0097]    In step  1305 , the storage interfaces  220  transfer the data segments to the buffer manager  205  one data segment at a time as the data segments are received from the respective storage devices  115 . In one embodiment, DMA engines of the storage interfaces  220  transfer the data segments to the buffer manager  205  based on transfer parameters provided by the controller  200 . Similar to the process described above with respect to  FIG. 11 , access to the buffer manager  205  is controlled via the switch  215  using an arbitration scheme performed by the controller  200 . In this way, the storage interfaces  220  are given alternating access to the buffer manager  205  for transferring data cells according to the arbitration scheme. The method then proceeds to step  1310 . 
         [0098]    In step  1310 , the data segments are reassembled in the buffer manager  205  into data for transfer to the host system  105 . In one embodiment, the buffer manager  205  reassembles data segments by storing data of the data segments together as they are transferred into buffer manager  205 . The method then proceeds to step  1315 . 
         [0099]    In step  1315 , the DMA engine of the host interface  210  transfers the data segments to the host system  105  using transfer parameters provided by the controller  200 . The controller  200  allocates access to the buffer manager  205  by the host interface  210  and the storage interfaces  220  by using an arbitration scheme, such as those described above. As with the data storage process of  FIG. 11 , the host interface  210  may begin transferring data to the host system  105  immediately upon buffer manager  205  receiving the first data segment from one of the storage interfaces  220 . Alternatively, the host interface  210  may wait until a minimum amount of data has been transferred to the buffer manager  205  from the storage devices  115 . In one embodiment, the controller  200  alternates access to the buffer manager  205  between the host interface  210  and the storage interfaces  220  based on an arbitration scheme. This portion of the method then ends. In one embodiment, the method then proceeds to step  1110  of  FIG. 10 . 
         [0100]      FIG. 14  illustrates a data transfer from the storage devices  115  to the host system  105 , in which data is read from the storage devices  115 , in accordance with an embodiment of the present invention. For example, the data transfer from the host system  105  to the storage devices  115 - a - d  may be a read operation. In the data transfer, the data management system  110  receives eight data segments  1402  (e.g., data segments  1402   a - h ) from the respective storage devices  115  substantially in parallel. The eight data segments are used as for exemplary illustrative purposes to describe the invention; however, in many data transfers would involve substantially more data segments. The data management system  110  receives a sequence  1400  of two data segments  1402   a  and  1402   e  from the storage device  115   a , a sequence  1405  of two data segments  1402   b  and  1402   f  from the storage device  115   b , a sequence  1410  of two data segments  1402   c  and  1402   g  from the storage device  115   c , and a sequence  1415  of two data segments  1402   d  and  1402   h  from the storage device  115   d . The data management system  110  begins to transfer the data segments  1402  received from the storage devices  115  to the host system  105  once the first data segment  1402  is received from the storage devices  115 . As illustrated in  FIG. 14 , the data management system  110  transfers a sequence  1420  of the data segments  1402  received from the storage devices  115  to the host system  105 . For example, the data management system  110  may transfer the sequence of data segments  1420  to the host system  105  during sequential time slots by transferring one data segment at a time during each time slot. 
         [0101]    The foregoing description of the present invention illustrates and describes the preferred embodiments of the present invention. However, it is to be understood that the present invention is capable of use in various other combinations and modifications within the scope of the inventive concepts as expressed herein, commensurate with the above teachings, and/or the skill or knowledge of the relevant art. The embodiments described hereinabove are further intended to explain the best modes known of practicing the present invention and to enable others skilled in the art to utilize the present invention in such, or other, embodiments and with the various modifications required by the particular applications or uses of the present invention. Accordingly, the description is not intended to limit the scope of the present invention, which should be interpreted using the appended claims.