Patent Publication Number: US-2023161748-A1

Title: Utilizing Metadata To Represent Data

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a continuation application for patent entitled to a filing date and claiming the benefit of earlier-filed U.S. Pat. No. 11,561,949, issued Jan. 24, 2023, herein incorporated by reference in its entirety, which is a continuation of U.S. Pat. No. 10,783,131, issued Sep. 22, 2020, which is a continuation of U.S. Pat. No. 9,864,769, issued Jan. 9, 2018. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     This invention relates to computer networks and, more particularly, to efficiently storing data in a storage system. 
     Description of the Related Art 
     As computer memory storage and data bandwidth increase, so does the amount and complexity of data that businesses daily manage. A distributed storage system may be coupled to client computers interconnected by one or more networks. If any portion of the distributed storage system has poor performance, company operations may be impaired. A distributed storage system therefore maintains high standards for data availability and high-performance functionality. 
     The distributed storage system comprises physical volumes, which may be solid-state devices or partitions of a storage device. Software applications, such as a logical volume manager or a disk array manager, provide a means of allocating space on mass-storage arrays. In addition, this software allows a system administrator to create units of storage groups including logical volumes. Storage virtualization provides an abstraction (separation) of logical storage from physical storage in order to access logical storage without end-users identifying physical storage. 
     To support storage virtualization, a volume manager performs input/output (I/O) redirection by translating incoming I/O requests using logical addresses from end-users into new requests using addresses associated with physical locations in the storage devices. As some storage devices may include additional address translation mechanisms, such as address translation layers that may be used in solid-state storage devices, the translation from a logical address to another address mentioned above may not represent the only or final address translation. Redirection utilizes metadata stored in one or more mapping tables. In addition, information stored in one or more mapping tables may be used for storage deduplication and mapping virtual sectors at a specific snapshot level to physical locations. As the amount of data to maintain in a storage system grows, the cost of storing the data likewise grows. 
     In view of the above, systems and methods for efficiently storing data in a storage system are desired. 
     SUMMARY OF THE INVENTION 
     Various embodiments of a computer system and methods for efficiently storing data in a storage system are contemplated. 
     In various embodiments, a data storage subsystem coupled to a network receives read and write requests on the network from a client computer. The data storage subsystem includes multiple data storage locations on multiple storage devices. The data storage subsystem also includes at least one mapping table. The mapping table includes a plurality of entries, with each of the entries including a tuple with a key. The entry may also include a pointer to a physical location within the multiple storage devices. 
     A data storage controller determines whether data to store in the storage subsystem has a repeating pattern. In some embodiments, repeating patterns are intermingled with non-pattern data. Rather than store the repeating pattern on the storage devices, the controller stores information in a header on the storage devices. The information provides an identification of the pattern and its location(s). In various embodiments, the information includes at least an offset for the first instance of the repeating pattern, a pattern length, and an identification of the pattern, and locations of the pattern data with respect to the intermingled non-pattern data. In this manner, multiple instances of the pattern need not be stored. Reads of the data result in reconstruction of the data from the information stored in the header. 
     These and other embodiments will become apparent upon consideration of the following description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a generalized block diagram illustrating one embodiment of network architecture. 
         FIG.  2    is a generalized block diagram of one embodiment of a data storage layout. 
         FIG.  3    is a generalized block diagram of another embodiment of a data storage layout. 
         FIG.  4    is a generalized block diagram of yet another embodiment of a data storage layout. 
         FIG.  5    is a generalized flow diagram of one embodiment of a method corresponding to a received write request. 
         FIG.  6    is a generalized flow diagram of one embodiment of a method corresponding to a received read request. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, numerous specific details are set forth to provide a thorough understanding of the present invention. However, one having ordinary skill in the art should recognize that the invention might be practiced without these specific details. In some instances, well-known circuits, structures, signals, computer program instruction, and techniques have not been shown in detail to avoid obscuring the present invention. 
     Referring to  FIG.  1   , a generalized block diagram of one embodiment of a network architecture  100  is shown. As described further below, one embodiment of network architecture  100  includes client computer systems  110   a - 110   b  interconnected to one another through a network  180  and to data storage arrays  120   a - 120   b.  Network  180  may be coupled to a second network  190  through a switch  140 . Client computer system  110   c  is coupled to client computer systems  110   a - 110   b  and data storage arrays  120   a - 120   b  via network  190 . In addition, network  190  may be coupled to the Internet  160  or otherwise outside network through switch  150 . 
     It is noted that in alternative embodiments, the number and type of client computers and servers, switches, networks, data storage arrays, and data storage devices is not limited to those shown in  FIG.  1   . At various times one or more clients may operate offline. In addition, during operation, individual client computer connection types may change as users connect, disconnect, and reconnect to network architecture  100 . Further, while the present description generally discusses network attached storage, the systems and methods described herein may also be applied to directly attached storage systems and may include a host operating system configured to perform one or more aspects of the described methods. Numerous such alternatives are possible and are contemplated. A further description of each of the components shown in  FIG.  1    is provided shortly. First, an overview of some of the features provided by the data storage arrays  120   a - 120   b  is described. 
     In the network architecture  100 , each of the data storage arrays  120   a - 120   b  may be used for the sharing of data among different servers and computers, such as client computer systems  110   a - 110   c.  In addition, the data storage arrays  120   a - 120   b  may be used for disk mirroring, backup and restore, archival and retrieval of archived data, and data migration from one storage device to another. In an alternate embodiment, one or more client computer systems  110   a - 110   c  may be linked to one another through fast local area networks (LANs) in order to form a cluster. Such clients may share a storage resource, such as a cluster shared volume residing within one of data storage arrays  120   a - 120   b.    
     Each of the data storage arrays  120   a - 120   b  includes a storage subsystem  170  for data storage. Storage subsystem  170  may comprise a plurality of storage devices  176   a - 176   m.  These storage devices  176   a - 176   m  may provide data storage services to client computer systems  110   a - 110   c.  Each of the storage devices  176   a - 176   m  uses a particular technology and mechanism for performing data storage. The type of technology and mechanism used within each of the storage devices  176   a - 176   m  may at least in part be used to determine the algorithms used for controlling and scheduling read and write operations to and from each of the storage devices  176   a - 176   m . For example, the algorithms may locate particular physical locations corresponding to the operations. In addition, the algorithms may perform input/output (I/O) redirection for the operations, removal of duplicate data in the storage subsystem  170 , and support one or more mapping tables used for address redirection and deduplication. 
     The logic used in the above algorithms may be included in one or more of a base operating system (OS)  132 , a volume manager  134 , within a storage subsystem controller  174 , control logic within each of the storage devices  176   a - 176   m,  or otherwise. Additionally, the logic, algorithms, and control mechanisms described herein may comprise hardware and/or software. 
     Each of the storage devices  176   a - 176   m  may be configured to receive read and write requests and comprise a plurality of data storage locations, each data storage location being addressable as rows and columns in an array. In one embodiment, the data storage locations within the storage devices  176   a - 176   m  may be arranged into logical, redundant storage containers or RAID arrays (redundant arrays of inexpensive/independent disks). 
     In some embodiments, each of the storage devices  176   a - 176   m  may include or be further coupled to storage consisting of solid-state memory to store persistent data. In one embodiment, the included solid-state memory comprises solid-state drive (SSD) technology. A Solid-State Disk (SSD) may also be referred to as a Solid-State Drive. 
     Storage array efficiency may be improved by creating a storage virtualization layer between user storage and physical locations within storage devices  176   a - 176   m.  In one embodiment, a virtual layer of a volume manager is placed in a device-driver stack of an operating system (OS), rather than within storage devices or in a network. A volume manager or a disk array manager is used to support device groups  173   a - 173   m.    
     In one embodiment, one or more mapping tables may be stored in the storage devices  176   a - 176   m,  rather than memory, such as RAM  172 , memory medium  130  or a cache within processor  122 . The storage devices  176   a - 176  may be SSDs utilizing Flash memory. The low read access and latency times for SSDs may allow a small number of dependent read operations to occur while servicing a storage access request from a client computer. The dependent read operations may be used to access one or more indexes, one or more mapping tables, and user data during the servicing of the storage access request. 
     The information within a mapping table may be compressed. A particular compression algorithm may be chosen to allow identification of individual components, such as a key within a record among multiple records. Therefore, a search for a given key among multiple compressed records may occur. If a match is found, only the matching record may be decompressed. Compressing data within records of a mapping table may further enable fine-grained level mapping. 
     Network architecture  100  includes client computer systems  110   a - 110   c  interconnected through networks  180  and  190  to one another and to data storage arrays  120   a - 120   b.  Networks  180  and  190  may include a variety of techniques including wireless connection, direct local area network (LAN) connections, wide area network (WAN) connections such as the Internet, a router, storage area network, Ethernet, and others. Networks  180  and  190  may comprise one or more LANs that may also be wireless. Switch  140  may utilize a protocol associated with both networks  180  and  190 . The network  190  may interface with a set of communications protocols used for the Internet  160  such as the Transmission Control Protocol (TCP) and the Internet Protocol (IP), or TCP/IP. Switch  150  may be a TCP/IP switch. 
     Client computer systems  110   a - 110   c  are representative of any number of stationary or mobile computers such as desktop personal computers (PCs), servers, server farms, workstations, laptops, handheld computers, servers, personal digital assistants (PDAs), smart phones, and so forth. Each of the client computer systems  110   a - 110   c  may include a hypervisor used to support virtual machines (VMs). 
     Each of the data storage arrays  120   a - 120   b  may be used for the sharing of data among different servers, such as the client computer systems  110   a - 110   c.  Each of the data storage arrays  120   a - 120   b  includes a storage subsystem  170  for data storage. Storage subsystem  170  may comprise a plurality of storage devices  176   a - 176   m.  Each of these storage devices  176   a - 176   m  may be an SSD. A controller  174  may comprise logic for handling received read/write requests. A random-access memory (RAM)  172  may be used to batch operations, such as received write requests. In various embodiments, when batching write operations (or other operations) non-volatile storage (e.g., NVRAM) may be used. 
     The base OS  132 , the volume manager  134  (or disk array manager  134 ), any OS drivers (not shown) and other software stored in memory medium  130  may provide functionality providing access to files and the management of these functionalities. The base OS  132  and the OS drivers may comprise program instructions stored on the memory medium  130  and executable by processor  122  to perform one or more memory access operations in storage subsystem  170  that correspond to received requests. Each of the data storage arrays  120   a - 120   b  may use a network interface  124  to connect to network  180 . Similar to client computer systems  110   a - 110   c,  in one embodiment, the functionality of network interface  124  may be included on a network adapter card. 
     In addition to the above, each of the storage controllers  174  within the data storage arrays  120   a - 120   b  may support storage array functions such as snapshots, replication and high availability. In addition, each of the storage controllers  174  may support a virtual machine environment that comprises a plurality of volumes with each volume including a plurality of snapshots. In one example, a storage controller  174  may support hundreds of thousands of volumes, wherein each volume includes thousands of snapshots. In one embodiment, a volume may be mapped in fixed-size sectors, such as a 4-kilobyte (KB) page within storage devices  176   a - 176   m.  In another embodiment, a volume may be mapped in variable-size sectors such as for write requests. A volume ID, a snapshot ID, and a sector number may be used to identify a given volume. 
     An address translation table may comprise a plurality of entries, wherein each entry holds a virtual-to-physical mapping for a corresponding data component. This mapping table may be used to map logical read/write requests from each of the client computer systems  110   a - 110   c  to physical locations in storage devices  176   a - 176   m.  A “physical” pointer value may be read from the mapping table during a lookup operation corresponding to a received read/write request. This physical pointer value may then be used to locate a physical location within the storage devices  176   a - 176   m.  It is noted the physical pointer value may be used to access another mapping table within a given storage device of the storage devices  176   a - 176   m.  Consequently, one or more levels of indirection may exist between the physical pointer value and a target storage location. 
     Referring to  FIG.  2   , a generalized block diagram of one embodiment of a data storage layout  200  is shown. As shown, write data  210  is received for storage in a data storage medium  230 . In the example shown, the write data  210  includes N subsets, wherein N is an integer. Each subset may correspond to a given storage unit size or subunit size depending on the particular storage architecture. The N subsets include non-pattern data  242  and repeating pattern data  240 . As shown, the non-pattern data  242  and the repeating pattern data  240  alternate among subsets within the write data  210 . However, the pattern and non-pattern data need not strictly alternate. Rather, other arrangements among the subsets are possible and contemplated. 
     In various embodiments, the number of bits in a detectable bit pattern may be programmable and the number of instances of a pattern to be detected may be programmable. For example, bit patterns of up to 4, 8, or some other number of bits may be identifiable. Numerous methods of identifying bit patterns are known in the art and are contemplated. For example, various embodiments may compare bits of data to predetermined patterns for identification. As a simple example, there are 16 possible combinations for a pattern of 4 bits (0000-1111). These 16 patterns could be maintained in a table, array, or otherwise. Alternatively, such patterns may be detected using binary logic. Still further, various forms of automata or state machines may be used to detect patterns. Numerous such approaches are possible and are contemplated. In some embodiments, detection logic may compare chunks of M-bytes where M is an integer greater than or equal to one. For example, the byte pattern 0x0A that repeats within a subset may be detected as a repeating pattern, where a single instance of the bit pattern 0x0A has a size of a byte. As used herein, the notation “0x” indicates a hexadecimal value. A comparison of a first byte and a contiguous second byte that results in a match (i.e., the bit pattern in the first byte matches that of the second) indicates at least a start of a repeating pattern. Similarly, a comparison of a first 2-byte value and a contiguous second 2-byte value that results in a match indicates at least a start of a repeating pattern. 
     In some embodiments, a programmable limit may be established for the maximum size of a pattern. For example, in an embodiment where a repeating pattern cannot exceed four bytes in size, a comparison of a first 4-byte value and a contiguous second 4-byte value that results in a match may indicate the start of a repeating pattern (i.e., a four byte pattern has been detected to occur twice). However, the pattern 0x12345678 0x12345678 that repeats within the subset would not be identified (or qualify) as a repeating pattern since the pattern length is 8 bytes. 
     In various embodiments, another limit or threshold may be used for the number of contiguous instances of a given pattern needed to qualify for a repeating pattern. For example, if such a threshold value is set at 4, four or more contiguous instances of a pattern would qualify as a repeating pattern, but two or three would not. In some embodiments, the threshold number of contiguous instances of the bit pattern need to qualify as a repeating pattern may be set to half of a subset. In yet other embodiments, the write request may include an indication and/or identification of patterns of data within a write request. The qualifications for identifying a series of repeating patterns may determine how the data is stored among the mapping table and the data storage. 
     In the example shown in  FIG.  2   , the repeating patterns in the write data  210  may represent a same pattern. For example, the subset 2, the subset 4, the subset N-2 and so forth, may each store the same repeating pattern data (e.g., instances of a same pattern, though not necessarily the same number of instances). Alternatively, one or more of the subsets in the write data  210  that store a repeating pattern may store a pattern different from other subsets. For example, the subset 2 may store a series of the repeating pattern 0x 26 26, whereas the subset 4 may store a series of the repeating pattern 0x 89AB 89AB. 
     When the write data  210  is written to the data storage medium  230 , each of a mapping table  220  and the data storage medium  230  may be updated. In the example shown, the mapping table  220  may typically include at least a key and a pointer. In one embodiment, the key may be an identifier for the write data  210  being stored in the data storage medium  230  and the pointer may be an identification (e.g., an address) corresponding to a location within the data storage medium  230  where the write data  210  is to be stored. For example, the data  210  may be stored as a block and the pointer may identifying an address (e.g., the beginning) of the block. In this example, the mapping table  220  has one entry corresponding to the write data  210  and all of the write data  210  is stored in the data storage medium  230 . 
     The data storage medium  230  may represent an entire allocated block for a write operation or a subset of the allocated block. As shown, the data storage medium  230  stores each of the subsets of the write data  210 . Additionally, the data storage medium  230  includes metadata  244 . The metadata  244  may store data protection information, such as intra-device protection data, checksums, and/or otherwise. The metadata  244  may store log data. Additionally, the metadata  244  may store data location information such as volume identifiers, sector numbers, data chunk and offset numbers, track numbers, and so forth. Although the metadata  244  is shown at the top of the data storage medium  230 , in other examples, the metadata  244  may be stored at the bottom of data storage medium  230 . Alternatively, the information in the metadata  244  may be distributed at the top or bottom of the data storage medium  230  and within headers in each of the subsets. 
     Turning now to  FIG.  3   , a generalized block diagram of another embodiment of a data storage layout  300  is shown improved data storage. In this embodiment, a mapping table  320  stores information identifying pattern data intermingled with non-pattern data. The non-pattern data is stored to a data storage medium  330 , while the pattern data is not. As shown, a write request again includes the write data  210 , which is to be stored in a data storage medium. Responsive to the write request, each of a mapping table  320  and the data storage medium  330  is updated. The mapping table  320  has multiple entries for the write data  210 . In the example shown, each of the N subsets within the write data  210  has a corresponding entry in the mapping table  320 . Each of the keys in the mapping table  320  is unique for a corresponding subset within the write data  210 . Similarly, each of the pointers in the mapping table  320  is unique for a corresponding subset within the write data  210 . 
     For subsets within the write data  210  that include a repeating pattern, the corresponding entries in the mapping table  320  store information identifying the pattern data. For example, one or more status fields may be set to indicate the stored data does not include a pointer value. Rather, at least an indication of the repeating pattern is stored. In various embodiments, a single instance of the pattern may be stored in an entry of the mapping table  320 , along with a number of instances of the pattern. For example, if Subset 2 stores a repeating pattern of twenty instances of 0x4, an identification of the pattern 0x4 may be stored in the entry for Subset 2 along with an identification of the number of instances (twenty). In the example shown, only the non-pattern data is stored in the storage medium  330  requiring only half the storage of the example of  FIG.  2   . 
     Referring now to  FIG.  4   , a generalized block diagram of yet another embodiment of a data storage layout  400  is shown. In this embodiment, the non-pattern data of the write data  210  is stored in the data storage medium as in  FIG.  3   . However, pattern identifying data is also stored in the data storage medium using the above described approach for reducing the amount of storage required. As shown, s write request includes the write data  210 , which is to be stored in a data storage medium. When the write data  210  is written to the data storage medium  430 , each of a mapping table  220  and the data storage medium  430  is updated. The mapping table  220  has one entry corresponding to the write data  210 . The key is an identifier for the write data  210  being stored in the data storage medium. The pointer is an address of a target physical location within the data storage medium where the write data  210  is to be stored. 
     In the example shown, as only the non-pattern data is generally stored in the medium  230  the data storage medium  430 , the required storage is approximately half that of  FIG.  2   . For subsets within the write data  210  that qualify as a series of repeating patterns, there may be no corresponding entries in the mapping table  220  as there were in  FIG.  3   . Additionally, there are no subsets in the data storage medium  430  allocated for the repeating pattern data. Rather, the metadata  444  within the data storage medium  430  stores identifications of repeating patterns. The information in the metadata  444  may store information as described earlier for metadata  144  in  FIG.  2   . Additionally, for each series of repeating patterns, the metadata  444  stores an identification of the pattern (e.g., a single instance of the pattern), a length of the series of the repeating pattern (or number of instances of a pattern), and an offset for the series of repeating patterns. 
     For example, subset 2 in the write data  210  may store a repeating pattern, such as 0x01 0x01. The metadata  444  may store a single instance of the pattern such as 0x01 or an instance of the repeating pattern 0x01 0x01. In addition, the metadata  444  may store an indication of a number of instances of the pattern or repeating pattern. Further, the metadata  444  may store an offset within the write data  210  of the repeating pattern. For example, if Subset 1 is at an offset of 0 in the write data  210 , Subset 2 is at an offset of 1, Subset 3 is an offset of 2, and so on. In various embodiments, the metadata also identifies an offset for each of the non-pattern subsets of data. In this manner, the relative locations of both the pattern and non-pattern are known and the original data  210  can be reconstructed as needed. In such a manner, the write data  210  may be efficiently stored in a data storage medium with the sizes of the corresponding mapping table  220  and the corresponding data storage medium  430  being reduced from the size of the write data  210 . In various embodiments, the efficient storage of the write data  210  may be performed in a distributed data storage system utilizing solid-state devices. For example, the network architecture  100  may use the efficient storage of the write data. 
     Turning now to  FIG.  5   , a generalized flow diagram of one embodiment of a method  500  corresponding to a received write request is shown. The components embodied in the data storage layouts and the network architecture  100  described above may generally operate in accordance with method  500 . For purposes of discussion, the steps in this embodiment are shown in sequential order. However, some steps may occur in a different order than shown, some steps may be performed concurrently, some steps may be combined with other steps, and some steps may be absent in another embodiment. 
     In block  502 , a write request is received. In some embodiments, an indication of a series of patterns is provided in the write request. In other embodiments, patterns of data are detected. For example, control logic may compare contiguous chunks of M-bytes, wherein matches indicate a pattern. In various embodiments, the control logic is within the data storage controller  174 , though it may be located elsewhere. The integer M may be any positive value from  1  to a limit, such as 4, in one example. A same byte pattern of 0x00 that repeats within a given subset may be detected as a repeating pattern. In some embodiments, the subset is a sector in a SSD. A comparison of a first portion of data and a contiguous second portion of data that results in a match indicates at least a start of a repeating pattern. 
     If the control logic does not detect the write data of the write request has a series of patterns intermingled with non-pattern data (conditional block  504 ), then in block  506 , a new mapping table entry is created with a pointer to (or other identification of) a location in the SSDs for the write data. Alternatively, if the entire write data is a series of patterns, the new mapping table entry includes an indication of the pattern. However, in other embodiments, the mapping table includes a pointer to the series of patterns in the write data and an identification of the pattern is stored in the storage medium rather than the actual entire write data. The write data may be the size of an allocated block that comprises a number of sectors. In some examples, the block includes 64 sectors. In other examples, the block includes 128 sectors. Any number of sectors, or subsets, may be used. 
     If the control logic does detect the write data of the write request has a series of patterns intermingled with non-pattern data (conditional block  504 ), and (in at least some embodiments) the size of the series of patterns is greater than a size threshold (conditional block  508 ), then in block  510 , the offsets for at least the repeating pattern in the write data is determined. In some embodiments, the offsets may use the granularity of a subset or a sector. An indication of the length of the pattern and the pattern itself may be stored with other metadata. In some embodiments, a stride of offsets for at least one repeating pattern is determined. The stride may also be stored with the pattern and the length of the pattern. A stride of offsets for the non-pattern data may be additionally determined and stored with the pattern and the length of the pattern. For example, if the repeating pattern data occurs every other subset (or other unit) as was shown in  FIG.  4   , then a stride of 2 may be used to indicate every other subset. In such an embodiment, storing an offset for every subset may not be needed. Rather, an offset of the first subset may be identified along with a stride and a number of subsets. In block  512 , one or more mapping table entries, each with a respective pointer for the corresponding non-pattern data, may be created. 
     In block  514 , header information is created with at least offsets, a possible stride of offsets, pattern lengths and patterns for the detected series of repeating patterns. Offsets or a stride of offsets for the non-pattern data may also be included. In block  516 , a write operation is performed to the storage medium for the mapping and header information and the non-pattern data. 
     Turning now to  FIG.  6   , a generalized flow diagram of one embodiment of a method  600  corresponding to a received read request is shown. The components embodied in the data storage layouts and the network architecture  100  described above may generally operate in accordance with method  600 . For purposes of discussion, the steps in this embodiment are shown in sequential order. However, some steps may occur in a different order than shown, some steps may be performed concurrently, some steps may be combined with other steps, and some steps may be absent in another embodiment. 
     In block  602 , a read request is received. A key generator may receive one or more requester data inputs. The received read request may identify a particular volume, sector and length. In block  604 , the key generator may produce a query key value that includes a volume identifier (ID), a logical or virtual address, a snapshot ID, and a sector number. Other combinations are possible and other or additional values may be utilized as well. In block  606 , different portions of the query key value may be compared to values stored in columns that may or may not be contiguous within a mapping table. In various embodiments, the mapping table is an address translation directory table. To provide the different portions of the query key value to the columns within the mapping table, one or more index tables were accessed beforehand. 
     In block  608 , an associated mapping table entry is obtained. The mapping table result is used in block  610  to perform a storage access that corresponds to the target location of the original read request. If stored header information corresponding to the read request indicates the read data has patterns intermingled with non-pattern data (conditional block  612 ), then in block  614 , the information such as offsets, strides of offsets, pattern lengths and patterns stored in the header information is used to reconstruct the requested data. Both non-pattern data and reconstructed pattern data may be combined to recreate the original write data. In block  616 , the data corresponding to the target location of the read request is sent to the requester. 
     It is noted that the above-described embodiments may comprise software. In such an embodiment, the program instructions that implement the methods and/or mechanisms may be conveyed or stored on a computer readable medium. Numerous types of media which are configured to store program instructions are available and include hard disks, floppy disks, CD-ROM, DVD, flash memory, Programmable ROMs (PROM), random access memory (RAM), and various other forms of volatile or non-volatile storage. 
     In various embodiments, one or more portions of the methods and mechanisms described herein may form part of a cloud-computing environment. In such embodiments, resources may be provided over the Internet as services according to one or more various models. Such models may include Infrastructure as a Service (IaaS), Platform as a Service (PaaS), and Software as a Service (SaaS). In IaaS, computer infrastructure is delivered as a service. In such a case, the computing equipment is generally owned and operated by the service provider. In the PaaS model, software tools and underlying equipment used by developers to develop software solutions may be provided as a service and hosted by the service provider. SaaS typically includes a service provider licensing software as a service on demand. The service provider may host the software, or may deploy the software to a customer for a given period of time. Numerous combinations of the above models are possible and are contemplated. 
     Although the embodiments above have been described in considerable detail, numerous variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. It is intended that the following claims be interpreted to embrace all such variations and modifications.