Patent Publication Number: US-9424175-B1

Title: System and method for improving cache performance

Description:
TECHNICAL FIELD 
     This disclosure relates to cache memory systems and, more particularly, to systems and methods for improving the performance of cache memory systems. 
     BACKGROUND 
     Storing and safeguarding electronic content is of paramount importance in modern business. Accordingly, various systems may be employed to protect such electronic content. 
     The use of solid-state storage devices is increasing in popularity. A solid state storage device is a content storage device that uses solid-state memory to store persistent content. A solid-state storage device may emulate (and therefore replace) a conventional hard disk drive. Additionally/alternatively, a solid state storage device may be used within a cache memory system. With no moving parts, a solid-state storage device largely eliminates (or greatly reduces) seek time, latency and other electromechanical delays and failures associated with a conventional hard disk drive. 
     SUMMARY OF DISCLOSURE 
     In a first implementation, a computer-implemented method of processing write requests includes receiving a write request on a first cache system, wherein the write request identifies new content to be written to a data array. A write request content identifier associated with the new content is compared to a plurality of content identifiers included within a content directory for the first cache system to determine if a matching content identifier exists. Each of the plurality of content identifiers is associated with a piece of previously-written content included within the first cache system. If a matching content identifier is identified, content on the data array is copied from a first location on the data array associated with the matching content identifier to a second location on the data array associated with the write request content identifier. 
     One or more of the following features may be included. If a matching content identifier is not identified: the new content may be written to the first cache system; the content directory may be modified to include the write request content identifier; and the new content may be provided to the data array. The write request content identifier may be generated for the new content. The write request content identifier may be a hash function of the new content to be written to the data array. The write request may identify a logical unit and a storage address for storing the new content within the data array. 
     If a matching content identifier is identified, an entry within the content directory that is associated with the matching content identifier may be modified to identify the logical storage unit and the storage address for storing the new content within the data array. The content directory for the first cache system may include a plurality of entries, wherein each of the plurality of entries is associated with a specific piece of previously-written content within the first cache system. Each of the plurality of entries within the content directory may identify: a logical storage unit and a storage address at which the specific piece of previously-written content is located within the storage array; a first cache address at which the specific piece of previously-written content is located within the first cache system, and a content identifier for the specific piece of previously-written content. 
     In another implementation, a computer program product resides on a computer readable medium that has a plurality of instructions stored on it. When executed by a processor, the instructions cause the processor to perform operations including receiving a write request on a first cache system, wherein the write request identifies new content to be written to a data array. A write request content identifier associated with the new content is compared to a plurality of content identifiers included within a content directory for the first cache system to determine if a matching content identifier exists. Each of the plurality of content identifiers is associated with a piece of previously-written content included within the first cache system. If a matching content identifier is identified, content on the data array is copied from a first location on the data array associated with the matching content identifier to a second location on the data array associated with the write request content identifier. 
     One or more of the following features may be included. If a matching content identifier is not identified: the new content may be written to the first cache system; the content directory may be modified to include the write request content identifier; and the new content may be provided to the data array. The write request content identifier may be generated for the new content. The write request content identifier may be a hash function of the new content to be written to the data array. The write request may identify a logical unit and a storage address for storing the new content within the data array. 
     If a matching content identifier is identified, an entry within the content directory that is associated with the matching content identifier may be modified to identify the logical storage unit and the storage address for storing the new content within the data array. The content directory for the first cache system may include a plurality of entries, wherein each of the plurality of entries is associated with a specific piece of previously-written content within the first cache system. Each of the plurality of entries within the content directory may identify: a logical storage unit and a storage address at which the specific piece of previously-written content is located within the storage array; a first cache address at which the specific piece of previously-written content is located within the first cache system, and a content identifier for the specific piece of previously-written content. 
     In another implementation, a computing system includes at least one processor and at least one memory architecture coupled with the at least one processor, wherein the computing system is configured to perform operations including receiving a write request on a first cache system, wherein the write request identifies new content to be written to a data array. A write request content identifier associated with the new content is compared to a plurality of content identifiers included within a content directory for the first cache system to determine if a matching content identifier exists. Each of the plurality of content identifiers is associated with a piece of previously-written content included within the first cache system. If a matching content identifier is identified, content on the data array is copied from a first location on the data array associated with the matching content identifier to a second location on the data array associated with the write request content identifier. 
     One or more of the following features may be included. If a matching content identifier is not identified: the new content may be written to the first cache system; the content directory may be modified to include the write request content identifier; and the new content may be provided to the data array. The write request content identifier may be generated for the new content. The write request content identifier may be a hash function of the new content to be written to the data array. The write request may identify a logical unit and a storage address for storing the new content within the data array. 
     If a matching content identifier is identified, an entry within the content directory that is associated with the matching content identifier may be modified to identify the logical storage unit and the storage address for storing the new content within the data array. The content directory for the first cache system may include a plurality of entries, wherein each of the plurality of entries is associated with a specific piece of previously-written content within the first cache system. Each of the plurality of entries within the content directory may identify: a logical storage unit and a storage address at which the specific piece of previously-written content is located within the storage array; a first cache address at which the specific piece of previously-written content is located within the first cache system, and a content identifier for the specific piece of previously-written content. 
     The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features and advantages will become apparent from the description, the drawings, and the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagrammatic view of a storage system and a data caching process coupled to a distributed computing network; 
         FIG. 2  is a diagrammatic view of the storage system of  FIG. 1 ; 
         FIG. 3  is a diagrammatic view of a data write request for use with the data caching process of  FIG. 1 ; 
         FIG. 4  is a diagrammatic view of a data read request for use with the data caching process of  FIG. 1 ; 
         FIG. 5  is a diagrammatic view of a content directory for use with the data caching process of  FIG. 1 ; 
         FIG. 6  is a first flow chart of the data caching process of  FIG. 1 ; 
         FIG. 7  is a second flow chart of the data caching process of  FIG. 1 ; 
         FIG. 8  is a third flow chart of the data caching process of  FIG. 1 ; 
         FIG. 9  is a fourth flow chart of the data caching process of  FIG. 1 ; and 
         FIG. 10  is a fifth flow chart of the data caching process of  FIG. 1 . 
     
    
    
     Like reference symbols in the various drawings indicate like elements. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     System Overview: 
     As will be appreciated by one skilled in the art, the present disclosure may be embodied as a method, system, or computer program product. Accordingly, the present disclosure may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a “circuit,” “module” or “system.” Furthermore, the present disclosure may take the form of a computer program product on a computer-usable storage medium having computer-usable program code embodied in the medium. 
     Any suitable computer usable or computer readable medium may be utilized. The computer-usable or computer-readable medium may be, for example but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, device, or propagation medium. More specific examples (a non-exhaustive list) of the computer-readable medium would include the following: an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a transmission media such as those supporting the Internet or an intranet, or a magnetic storage device. Note that the computer-usable or computer-readable medium could even be paper or another suitable medium upon which the program is printed, as the program can be electronically captured, via, for instance, optical scanning of the paper or other medium, then compiled, interpreted, or otherwise processed in a suitable manner, if necessary, and then stored in a computer memory. In the context of this document, a computer-usable or computer-readable medium may be any medium that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device. The computer-usable medium may include a propagated data signal with the computer-usable program code embodied therewith, either in baseband or as part of a carrier wave. The computer usable program code may be transmitted using any appropriate medium, including but not limited to the Internet, wireline, optical fiber cable, RF, etc. 
     Computer program code for carrying out operations of the present disclosure may be written in an object oriented programming language such as Java, Smalltalk, C++ or the like. However, the computer program code for carrying out operations of the present disclosure may also be written in conventional procedural programming languages, such as the “C” programming language or similar programming languages. The program code may execute entirely on the user&#39;s computer, partly on the user&#39;s computer, as a stand-alone software package, partly on the user&#39;s computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user&#39;s computer through a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider). 
     The present disclosure is described below with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the disclosure. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks. 
     These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function/act specified in the flowchart and/or block diagram block or blocks. 
     The computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks. 
     System Overview: 
     Referring to  FIG. 1 , there is shown data caching process  10  that may reside on and may be executed by storage system  12 , which may be connected to network  14  (e.g., the Internet or a local area network). Examples of storage system  12  may include, but are not limited to: a Network Attached Storage (NAS) system, a Storage Area Network (SAN), a personal computer with a memory system, a server computer with a memory system, and a cloud-based device with a memory system. 
     As is known in the art, a SAN may include one or more of a personal computer, a server computer, a series of server computers, a mini computer, a mainframe computer, a RAID device and a NAS system. The various components of storage system  12  may execute one or more operating systems, examples of which may include but are not limited to: Microsoft Windows XP Server™; Novell Netware™; Redhat Linux™, Unix, or a custom operating system, for example. 
     The instruction sets and subroutines of data caching process  10 , which may be stored on storage device  16  included within storage system  12 , may be executed by one or more processors (not shown) and one or more memory architectures (not shown) included within storage system  12 . Storage device  16  may include but is not limited to: a hard disk drive; a tape drive; an optical drive; a RAID device; a random access memory (RAM); a read-only memory (ROM); and all forms of flash memory storage devices. 
     Network  14  may be connected to one or more secondary networks (e.g., network  18 ), examples of which may include but are not limited to: a local area network; a wide area network; or an intranet, for example. 
     Various data requests (e.g. data request  20 ) may be sent from client applications  22 ,  24 ,  26 ,  28  to storage system  12 . Examples of data request  20  may include but are not limited to data write requests (i.e. a request that content be written to storage system  12 ) and data read requests (i.e. a request that content be read from storage system  12 ). 
     The instruction sets and subroutines of client applications  22 ,  24 ,  26 ,  28 , which may be stored on storage devices  30 ,  32 ,  34 ,  36  (respectively) coupled to client electronic devices  38 ,  40 ,  42 ,  44  (respectively), may be executed by one or more processors (not shown) and one or more memory architectures (not shown) incorporated into client electronic devices  38 ,  40 ,  42 ,  44  (respectively). Storage devices  30 ,  32 ,  34 ,  36  may include but are not limited to: hard disk drives; tape drives; optical drives; RAID devices; random access memories (RAM); read-only memories (ROM), and all forms of flash memory storage devices. Examples of client electronic devices  38 ,  40 ,  42 ,  44  may include, but are not limited to, personal computer  38 , laptop computer  40 , personal digital assistant  42 , notebook computer  44 , a server (not shown), a data-enabled, cellular telephone (not shown), and a dedicated network device (not shown). 
     Users  46 ,  48 ,  50 ,  52  may access storage system  12  directly through network  14  or through secondary network  18 . Further, storage system  12  may be connected to network  14  through secondary network  18 , as illustrated with link line  54 . 
     The various client electronic devices may be directly or indirectly coupled to network  14  (or network  18 ). For example, personal computer  38  is shown directly coupled to network  14  via a hardwired network connection. Further, notebook computer  44  is shown directly coupled to network  18  via a hardwired network connection. Laptop computer  40  is shown wirelessly coupled to network  14  via wireless communication channel  56  established between laptop computer  40  and wireless access point (i.e., WAP)  58 , which is shown directly coupled to network  14 . WAP  58  may be, for example, an IEEE 802.11a, 802.11b, 802.11g, 802.11n, Wi-Fi, and/or Bluetooth device that is capable of establishing wireless communication channel  56  between laptop computer  40  and WAP  58 . Personal digital assistant  42  is shown wirelessly coupled to network  14  via wireless communication channel  60  established between personal digital assistant  42  and cellular network/bridge  62 , which is shown directly coupled to network  14 . 
     As is known in the art, all of the IEEE 802.11x specifications may use Ethernet protocol and carrier sense multiple access with collision avoidance (i.e., CSMA/CA) for path sharing. The various 802.11x specifications may use phase-shift keying (i.e., PSK) modulation or complementary code keying (i.e., CCK) modulation, for example. As is known in the art, Bluetooth is a telecommunications industry specification that allows e.g., mobile phones, computers, and personal digital assistants to be interconnected using a short-range wireless connection. 
     Client electronic devices  38 ,  40 ,  42 ,  44  may each execute an operating system, examples of which may include but are not limited to Microsoft Windows™, Microsoft Windows CE™, Redhat Linux™, or a custom operating system. 
     The Data Caching Process: 
     For the following discussion, client application  22  is going to be described for illustrative purposes. However, this is not intended to be a limitation of this disclosure, as other client applications (e.g., client applications  24 ,  26 ,  28 ) may be equally utilized. 
     For illustrative purposes, storage system  12  will be described as being a network-based storage system that includes a plurality of electro-mechanical backend storage devices. However, this is for illustrative purposes only and is not intended to be a limitation of this disclosure, as other configurations are possible and are considered to be within the scope of this disclosure. For example and as discussed above, storage system  12  may be a personal computer that includes a single electro-mechanical storage device. 
     Referring also to  FIG. 2 , storage system  12  may include a server computer/controller (e.g. server computer/controller  100 ), and a plurality of storage targets T 1-n  (e.g. storage targets  102 ,  104 ,  106 ,  108 ). Storage targets  102 ,  104 ,  106 ,  108  may be configured to provide various levels of performance and/or high availability. For example, one or more of storage targets  102 ,  104 ,  106 ,  108  may be configured as a RAID 0 array, in which data is striped across storage targets. By striping data across a plurality of storage targets, improved performance may be realized. However, RAID 0 arrays do not provide a level of high availability. Accordingly, one or more of storage targets  102 ,  104 ,  106 ,  108  may be configured as a RAID 1 array, in which data is mirrored between storage targets. By mirroring data between storage targets, a level of high availability is achieved as multiple copies of the data are stored within storage system  12 . 
     While storage targets  102 ,  104 ,  106 ,  108  are discussed above as being configured in a RAID 0 or RAID 1 array, this is for illustrative purposes only and is not intended to be a limitation of this disclosure, as other configurations are possible. For example, storage targets  102 ,  104 ,  106 ,  108  may be configured as a RAID 3, RAID 4, RAID 5 or RAID 6 array. 
     While in this particular example, storage system  12  is shown to include four storage targets (e.g. storage targets  102 ,  104 ,  106 ,  108 ), this is for illustrative purposes only and is not intended to be a limitation of this disclosure. Specifically, the actual number of storage targets may be increased or decreased depending upon e.g. the level of redundancy/performance/capacity required. 
     Storage system  12  may also include one or more coded targets  110 . As is known in the art, a coded target may be used to store coded data that may allow for the regeneration of data lost/corrupted on one or more of storage targets  102 ,  104 ,  106 ,  108 . An example of such a coded target may include but is not limited to a hard disk drive that is used to store parity data within a RAID array. 
     While in this particular example, storage system  12  is shown to include one coded target (e.g., coded target  110 ), this is for illustrative purposes only and is not intended to be a limitation of this disclosure. Specifically, the actual number of coded targets may be increased or decreased depending upon e.g. the level of redundancy/performance/capacity required. 
     Examples of storage targets  102 ,  104 ,  106 ,  108  and coded target  110  may include one or more electro-mechanical hard disk drives, wherein a combination of storage targets  102 ,  104 ,  106 ,  108  and coded target  110  may form non-volatile, electro-mechanical memory system  112 . 
     The manner in which storage system  12  is implemented may vary depending upon e.g. the level of redundancy/performance/capacity required. For example, storage system  12  may be a RAID device in which server computer/controller  100  is a RAID controller card and storage targets  102 ,  104 ,  106 ,  108  and/or coded target  110  are individual “hot-swappable” hard disk drives. An example of such a RAID device may include but is not limited to an NAS device. Alternatively, storage system  12  may be configured as a SAN, in which server computer/controller  100  may be e.g., a server computer and each of storage targets  102 ,  104 ,  106 ,  108  and/or coded target  110  may be a RAID device and/or computer-based hard disk drive. Further still, one or more of storage targets  102 ,  104 ,  106 ,  108  and/or coded target  110  may be a SAN. 
     In the event that storage system  12  is configured as a SAN, the various components of storage system  12  (e.g. server computer/controller  100 , storage targets  102 ,  104 ,  106 ,  108 , and coded target  110 ) may be coupled using network infrastructure  114 , examples of which may include but are not limited to an Ethernet (e.g., Layer  2  or Layer  3 ) network, a fiber channel network, an InfiniBand network, or any other circuit switched/packet switched network. 
     Storage system  12  may execute all or a portion of data caching process  10 . The instruction sets and subroutines of data caching process  10 , which may be stored on a storage device (e.g., storage device  16 ) coupled to server computer/controller  100 , may be executed by one or more processors (not shown) and one or more memory architectures (not shown) included within server computer/controller  100 . Storage device  16  may include but is not limited to: a hard disk drive; a tape drive; an optical drive; a RAID device; a random access memory (RAM); a read-only memory (ROM); and all forms of flash memory storage devices. 
     As discussed above, various data requests (e.g. data request  20 ) may be generated. For example, these data requests may be sent from client applications  22 ,  24 ,  26 ,  28  to storage system  12 . Additionally/alternatively and when server computer/controller  100  is configured as an application server, these data requests may be internally generated within server computer/controller  100 . Examples of data request  20  may include but are not limited to data write request  116  (i.e. a request that content  118  be written to storage system  12 ) and data read request  120  (i.e. a request that content  118  be read from storage system  12 ). 
     Server computer/controller  100  may include input-output logic  122  (e.g., a network interface card), processing logic  124 , and first cache system  126 . Examples of first cache system  126  may include but are not limited to a volatile, solid-state, cache memory system (e.g., a dynamic RAM cache memory system) and/or a non-volatile, solid-state, cache memory system (e.g., a flash-based, cache memory system). 
     During operation of server computer/controller  100 , content  118  to be written to storage system  12  may be received by input-output logic  122  (e.g. from network  14  and/or network  18 ) and processed by processing logic  124 . Additionally/alternatively and when server computer/controller  100  is configured as an application server, content  118  to be written to storage system  12  may be internally generated by server computer/controller  100 . As will be discussed below in greater detail, processing logic  124  may initially store content  118  within first cache system  126 . 
     Depending on the manner in which first cache system  126  is configured, processing logic  124  may immediately write content  118  to second cache system  128 /non-volatile, electro-mechanical memory system  112  (if first cache system  126  is configured as a write-through cache) or may subsequently destage content  118  to second cache system  128 /non-volatile, electro-mechanical memory system  112  (if first cache system  126  is configured as a write-back cache). Additionally and in certain configurations, processing logic  124  may calculate and store coded data on coded target  110  (included within non-volatile, electromechanical memory system  112 ) that may allow for the regeneration of data lost/corrupted on one or more of storage targets  102 ,  104 ,  106 ,  108 . For example, if processing logic  124  was included within a RAID controller card or a NAS/SAN controller, processing logic  124  may calculate and store coded data on coded target  110 . However, if processing logic  124  was included within e.g., an applications server, data array  130  may calculate and store coded data on coded target  110 . 
     The combination of second cache system  128  and non-volatile, electromechanical memory system  112  may form data array  130 , wherein first cache system  126  may be sized so that the number of times that data array  130  is accessed may be reduced. Accordingly, by sizing first cache system  126  so that first cache system  126  retains a quantity of data sufficient to satisfy a significant quantity of data requests (e.g., data request  20 ), the overall performance of storage system  12  may be enhanced. As will be described below in greater detail, first cache system  126  may be a content-aware cache system. 
     Further, second cache system  128  within data array  130  may be sized so that the number of times that non-volatile, electromechanical memory system  112  is accessed may be reduced. Accordingly, by sizing second cache system  128  so that second cache system  128  retains a quantity of data sufficient to satisfy a significant quantity of data requests (e.g., data request  20 ), the overall performance of storage system  12  may be enhanced. As will be described below in greater detail, second cache system  130  may be a content-aware cache system. 
     As discussed above, the instruction sets and subroutines of data caching process  10 , which may be stored on storage device  16  included within storage system  12 , may be executed by one or more processors (not shown) and one or more memory architectures (not shown) included within storage system  12 . Accordingly, in addition to being executed on server computer/controller  100 , some or all of the instruction sets and subroutines of data caching process  10  may be executed by one or more processors (not shown) and one or more memory architectures (not shown) included within data array  130 . 
     Referring also to  FIGS. 3-4 , data request  20  (e.g. data read request  116  and/or data write request  120 ) may be processed by server computer/controller  100  to extract pertinent information concerning these data requests. 
     When data request  20  is a data write request (e.g., write request  116 ), write request  116  may include content  118  to be written to data array  130 . Additionally, write request  116  may include a storage address  200  that defines the intended storage location within storage array  130  at which content  118  is to be stored. For example, storage address  200  may define a particular logical unit within data array  130  (e.g., a LUN or Logical Unit Number) and a particular storage address within that specific logical unit (e.g., an LBA or Logical Block Address) for storing content  118 . 
     Concerning read request  120 , these requests do not include any content to be written to data array  130 , as these are read requests and concern content to be read from data array  130 . Read request  120  may include a storage address  202  that defines the storage location within storage array  130  from which content is to be retrieved. For example, storage address  202  may define a particular logical unit within data array  130  (e.g., a LUN or Logical Unit Number) and a particular storage address within that specific logical unit (e.g., an LBA or Logical Block Address) for retrieving the content sought from data array  130 . 
     As will be discussed below in greater detail and referring also to  FIG. 5 , data caching process  10  may maintain content directory  250 , which may be used to locate various pieces of content within first cache system  126 . In one particular embodiment of content directory  250 , content directory  250  may include plurality of entries  252 , wherein each of these entries may identify: data array storage address  200 / 202  (e.g. a logical storage unit and a storage address at which a specific piece of previously-written content is located within storage array  130 ); first cache address  254  (e.g., the location within first cache system  126  at which the specific piece of previously-written content is also located), and content identifier  256  for the specific piece of previously-written content. Accordingly, content directory  250  may identify the location of specific pieces of content included within first cache system  126  and their corresponding pieces of data within data array  130 , as well as a content identifier that uniquely identifies the specific piece of content. 
     Content identifier  256  may be a mathematical representation of the specific piece of previously-written content that may allow e.g. server computer/controller  100  to quickly determine whether two pieces of previously-written content are identical, as identical pieces of content would have identical content identifiers. In one particular embodiment, content identifier  256  may be a hash function (e.g., a cryptographic hash) of the previously-written content. 
     Compression Ratio Monitoring: 
     Data caching process  10  may be configured to compress the data stored on data array  130  to conserve storage space if computationally desirable. 
     Referring also to  FIG. 6 , data caching process  10  may be configured to receive  300  read request  120  on first cache system  126 , wherein read request  120  identifies previously-written content (as defined by storage address  202 ) included within data array  130 . For example, assume that user  46  is using client application  22  to access data (i.e. content  132 ) that is currently being stored on data array  130 . Accordingly, client application  22  may generate read request  120  which, as discussed above, may define a particular logical unit within data array  130  (e.g., a LUN or Logical Unit Number) and a particular storage address within that specific logical unit (e.g., an LBA or Logical Block Address) for retrieving content  132  sought from data array  130  by client application  22 . 
     Assume that read request  120  defines LUN 0 /LBA 5  as the location of content  132  within data array  130 . Upon receiving  300  read request  120 , data caching process  10  may compare the location of content  132  within data array  130  (namely LUN 0 /LBA 5 ) with each of the plurality of entries  252  defined within content directory  250  to determine if a copy of content  132  is locally available (i.e., cached) within first cache system  126 . If LUN 0 /LBA 5  was defined within content directory  250  (meaning that a local cached copy of content  132  is present/available within first cache system  126 ), that particular entry would also define a corresponding first cache address (e.g. first cache address  254 ) within first cache system  126  at which content  132  would be locally-available and retrievable from the first cache system  126 . Conversely, in the event that LUN 0 /LBA 5  is not defined within content directory  250  (meaning that a local cached copy of content  132  is not present/available within first cache system  126 ), data caching process  10  may need to obtain  302  content  132  identified in read request  120  from data array  130 . In this particular example, since LUN 0 /LBA 5  is not defined within content directory  250 , a local cached copy of content  132  is not present/available within first cache system  126  and data caching process  10  will be need to obtain  302  content  132  from data array  130 . 
     Once content  132  is obtained  302  by data caching process  10 , data caching process  10  may compress  304  content  132  prior to content  132  being stored within first cache system  126 , thus generating compressed content  134  which may be stored within (and conserve the storage space of) first cache system  126 . When compressing  304  content  132  to generate compressed content  134 , data caching process  10  may determine  306  compression ratio  136  for compressed content  134 . For example, if content  132  is 1.00 MB in size and compressed content  134  is 200 kB in size, data caching process  10  may determine  306  compression ratio  136  of 5:1 for compressed content  134 . Data caching process  10  may provide  308  compression ratio  136  to data array  130 . 
     Upon receiving compression ratio  136 , data caching process  10  may compare compression ratio  136  to a predefined threshold to determine whether content  132  (stored on data array  130 ) should be compressed  310 . For example, assume for illustrative purposes that this predefined threshold is 3:1, wherein if the compression ratio is less than 3:1, content  132  (stored on data array  130 ) would not be compressed  310  by data caching process  10 , as the computational expense of compressing content  132  (for storage on data array  130 ) would not be offset by the space savings achieved. However, if the compression ratio is greater than or equal to 3:1, data caching process  10  would compress  310  content  132 , as the space savings achieved on data array  130  would offset the computational expense of compressing content  132 . 
     As discussed above, data array  130  may include second cache system  128 . Accordingly, if data caching process  10  compresses  310  content  132  on data array  130 , if data array  130  also includes second cache system  128 , compressing  310  content  132  may also include/may alternatively include compressing  312  any cached copies of content  132  stored on second cache system  128 . 
     Uncompressed Data Retrieval: 
     Data caching process  10  may be configured to minimize/reduce processor loading by intelligently determining whether to decompress cached files or obtain uncompressed versions of those cached files. 
     Referring also to  FIG. 7 , data caching process  10  may be configured to receive  350  read request  120  on first cache system  126 , wherein read request  120  identifies previously-written content (e.g., content  132 ) included within data array  130 . Data caching process  10  may determine  352  if content  132  (identified in read request  120 ) is locally stored within first cache system  126  in a compressed format (e.g., as compressed content  132 ), and if content  132  (identified in read request  120 ) is stored within data array  130  in an uncompressed format (e.g., as content  132 ). 
     If it is determined  352  that the previously-written content requested in read request  120  is available locally (from first cache system  126 ) in a compressed format (e.g., compressed content  134 ) and is available remotely (from data array  130 ) in an uncompressed format (e.g., content  132 ), data caching process  10  may determine  354  if it is less computationally expensive to obtain previously-written content requested in read request  120  from data array  130  in an uncompressed format (e.g., content  132 ). Specifically, it may consume considerable processing power to decompress compressed content. Accordingly, when a compressed copy (e.g., compressed content  134 ) of the previously-written content requested in read request  120  is available locally (e.g. from first cache system  126 ) and an uncompressed copy (e.g., content  132 ) of the previously-written content requested in read request  120  is available remotely (e.g. from data array  130 ), it may consume less processing power to obtain the uncompressed copy of the previously-written content requested in read request  120  from data array  130  then it would consume to decompress the compressed copy of the previously-written content requested in read request  120  from first cache system  126 . 
     There are many factors that data caching process  10  may take into consideration when making determination  354 . For example, the compression ratio (as discussed above) of the compressed content may be taken into consideration when making determination  354 , as content having higher compression ratios may be more computationally expensive to decompress than content having lower compression ratios. Additionally, the current level of network traffic between data array  130  and server computer/controller  100  may be taken into consideration, as additional loading of a crowded network may be deemed undesirable by data caching process  10 . Further, the level of loading of the processor(s) included within server computer/controller  100  may be taken into consideration by data caching process  10 , as additional loading of the processor(s) included within server computer/controller  100  may be deemed undesirable by data caching process  10 . Additionally, the level of loading of the processor(s) included within data array  130  may be taken into consideration by data caching process  10 , as additional loading of the processor(s) included within data array  130  may be deemed undesirable by data caching process  10   
     If data caching process  10  determines  354  that it is less computationally expensive to obtain the previously-written content requested in read request  120  in an uncompressed format (e.g., content  132 ) from data array  130 , data caching process  10  may obtain  356  the uncompressed content (e.g., content  132 ) stored within data array  130 . 
     If data caching process  10  determines  354  that it is not less computationally expensive to obtain the previously-written content requested in read request  120  in an uncompressed format (e.g., content  132 ) from data array  130 , data caching process  10  may decompress  358  the compressed content (e.g., compressed content  134 ) stored within first cache system  126 . 
     As discussed above, data array  130  may include second cache system  128 . Accordingly, when data caching process  10  determines  352  that the previously-written content requested in read request  120  is available locally (from first cache system  126 ) in a compressed format (e.g., compressed content  134 ) and is available remotely (from data array  130 ) in an uncompressed format (e.g., content  132 ), data caching process  10  may also/alternatively determine  360  if the previously-written content identified in read request  120  is stored within second cache system  128  of data array  130  in an uncompressed format. 
     Backend Content Copy: 
     Data caching process  10  may be configured to minimize/reduce network loading by intelligently determining whether data located in data array  130  should be copied from a first location to a second location within data array  130  (as opposed to being transmitted over network infrastructure  114 ). 
     Referring also to  FIG. 8 , data caching process  10  may be configured to receive  400  write request  116  on first cache system  126 , wherein write request  116  identifies new content (e.g., content  118 ) to be written to data array  130 . 
     As discussed above, data write request  116  may include a storage address  200  that defines the intended storage location within storage array  130  at which content  118  is to be stored. For example, storage address  200  may define a particular logical unit within data array  130  (e.g., a LUN or Logical Unit Number) and a particular storage address within that specific logical unit (e.g., an LBA or Logical Block Address) for storing content  118 . 
     As discussed above, a content identifier (e.g., content identifier  256 ) may be a mathematical representation of a specific piece of content that may allow e.g. server computer/controller  100  to quickly determine whether two pieces of content are identical, as identical pieces of content would have identical content identifiers. 
     In one particular embodiment, content identifier  256  may be a hash function of the content. Upon receiving  400  write request  116  and content  118 , data caching process  10  may generate  402  content identifier  256  for content  118 . As discussed above, content identifier  256  generated  402  for the content (i.e., content  118 ) identified within write request  116  may be a hash function (e.g., a cryptographic hash) of content  118 . 
     As is known in the art, a hash function is an algorithm/subroutine that maps large data sets to smaller data sets. The values returned by a hash function are typically called hash values, hash codes, hash sums, checksums or simply hashes. Hash functions are mostly used to accelerate table lookup or data comparison tasks such as e.g., finding items in a database and detecting duplicated or similar records in a large file. 
     For example, assume for illustrative purposes that write request  116  includes storage address  200  that defines the intended storage location for content  118  as LUN 0 /LBA 0 . Accordingly, upon receiving  400  write request  116 , data caching process  10  may generate  402  content identifier  256  for content  118 . Assume for illustrative purposes that data caching process  10  generates a hash of content  118 , resulting in the generation  402  of content identifier  256  (namely hash value acdfcla). 
     This newly-generated content identifier  256  (i.e. acdfcla) associated with content  118  may be compared  404  to each of the other content identifiers (namely abalabz, alazcha, abalabz, alazcha) included within content directory  250  for first cache system  126  to determine if the newly-generated content identifier  256  (i.e. acdfcla) matches any of the other content identifiers (namely abalabz, alazcha, abalabz, alazcha) included within content directory  250 . 
     As discussed above, each entry of the plurality of entries  252  included within content directory  250  is associated with a unique piece of content included within first cache system  126 . Accordingly, each unique content identifier included within content directory  250  may be associated with a unique piece of content written to first cache system  126 . 
     If, when performing comparison  404 , data caching process  10  does not identify a content identifier (i.e., abalabz, alazcha, abalabz, alazcha) within content directory  250  that matches the above-described, newly-generated content identifier (i.e. acdfcla), data caching process  10  may write  406  content  118  to first cache system  126  and may provide  408  a copy of content  118  to data array  130  for storage within data array  130 . Additionally, data caching process  10  may modify  410  content directory  250  to include a new entry (i.e., entry  258 ) that defines the newly-generated content identifier (i.e. acdfcla), the location of content  118  within first cache system  126  (i.e., 001011), and the location of content  118  within data array  130  (i.e., LUN 0 /LBA 0 ). 
     If, when performing comparison  404 , data caching process  10  identified a content identifier within content directory  250  that matched the above-described, newly-generated content identifier (i.e. acdfcla), data caching process  10  would perform differently. 
     Accordingly, further assume for illustrative purposes that a second write request (i.e., write request  116 ′) includes storage address  200 ′ that defines the intended storage location for content  118 ′ as LUN 0 /LBA 1 . Accordingly, upon receiving  400  write request  116 ′, data caching process  10  may generate  402  content identifier  256  for content  118 ′. Assume for illustrative purposes that data caching process  10  generates a hash of content  118 ′, resulting in the generation  402  of content identifier  256  (namely hash value alazcha). 
     This newly-generated content identifier  256  (i.e. alazcha) associated with content  118 ′ may be compared  404  to each of the other content identifiers (namely abalabz, alazcha, abalabz, alazcha) included within content directory  250  for first cache system  126  to determine if the newly-generated content identifier  256  (i.e. alazcha) matches any of the other content identifiers (namely abalabz, alazcha, abalabz, alazcha) included within content directory  250 . 
     If, when performing comparison  404 , data caching process  10  does identify a content identifier (namely alazcha) within content directory  250  that matches the above-described, newly-generated content identifier (i.e. alazcha), data caching process  10  may perform a couple of functions. 
     For example, data caching process  10  may copy  412  content on data array  130  from a first location (namely LUN 4 /LBA 7 ) on data array  130  associated with the matching content identifier to a second location (namely LUN 0 /LBA 1 ) on data array  130  associated with the newly-generated content identifier. Specifically and for the reasons discussed above, since data caching process  10  identified matching content identifiers (i.e., having the same value of alazcha), content  118 ′ must be identical to the content stored at LUN 4 /LBA 7 . Accordingly, instead of transmitting content  118 ′ from server computer/controller  100  to data array  130 , data caching process  10  may simply effectuate on data array  130  a copy of the data currently stored at LUN 4 /LBA 7  to LUN 0 /LBA 1 , thus freeing up server computer/controller  100  to perform other functions and reducing network traffic on network infrastructure  114 . 
     Further, data caching process  10  may modify  414  the entry (i.e., entry  260 ) within content directory  250  that is associated with the matching content identifier (i.e., alazcha) to include storage address  200 ′ that defines the intended storage location for content  118 ′ (i.e., LUN 0 /LBA 1  within data array  130 ), thus generating modified entry  260 ′. Accordingly, modified entry  260  identifies that the pieces of content that are currently stored at LUN 4 /LBA 7  and LUN 0 /LBA 1  within data array  130  are identical. Accordingly, a single piece of cached content (located first cache address 010111 within first cache system  126 ) may be used as a local cached copy for both pieces of content stored on data array  130 . 
     Content Identifier Backend Retrieval: 
     Data caching process  10  may be configured to minimize/reduce loading of server computer/controller  100  by determining if content already exists on first cache system  126  before retrieving the same from data array  130 . 
     Referring also to  FIG. 9 , data caching system  10  may be configured to receive  450  read request  120  on first cache system  126 , wherein read request  120  identifies previously-written content (e.g., content  132 ) included within data array  130 . Upon receiving  450  read request  120 , data caching process  10  may process read request  120  to determine if content  132  is locally available within first cache system  126 . 
     As discussed above, read request  120  may define a particular logical unit within data array  130  (e.g., a LUN or Logical Unit Number) and a particular storage address within that specific logical unit (e.g., an LBA or Logical Block Address) for retrieving content  132  sought from data array  130 . 
     As discussed above, content directory  250  may include plurality of entries  252 , wherein each of these entries may identify: data array storage address  200 / 202  (e.g. a logical storage unit and a storage address at which a specific piece of previously-written content is located within storage array  130 ); first cache address  254  (e.g., the location within first cache system  126  at which the specific piece of previously-written content is also located), and content identifier  256  for the specific piece of previously-written content. 
     Accordingly, when data caching process  10  processes read request  120  to determine if content  132  is available within first cache system  126 , data caching process  10  may review content directory  250  to see if the LUN and LBA defined within read request  120  is listed within content directory  250 . 
     Assume for illustrative purposes that read request  120  is requesting the data stored at LUN 6 /LBA 4  of data array  130 . As LUN 6 /LBA 4  is not listed as a data array storage address  200 / 202  within content directory  250 , data caching process  10  will determine that the content requested in read request  120  is not available locally (i.e. from first cache system  126 ). 
     Accordingly, data caching process  10  may request  452 , from the data array, the content identifier for the content identified in the read request (namely content  132 ). Upon receiving request  452  from data caching process  10 , data array  130  may either a) retrieve the content identifier for the content identified in read request  120  (if previously generated and stored within e.g. a content directory (not shown) for second cache system  128 ; or b) generate the content identifier for the content identified in the read request  120  (as data array  130  has access to content  132 ). Once generated/retrieved by data array  130 , content identifier  138  may be received  454  by data caching process  10  from data array  130 . As discussed above, content identifier  138  may be a hash function of the content requested in data request  120  (namely content  132 ). 
     Data caching process  10  may compare  456  content identifier  138  (i.e., the content identifier associated with the content identified within read request  120 , namely content  132 ) to each of the content identifiers (namely abalabz, alazcha, abalabz, alazcha) included within content directory  250  for first cache system  126  to determine if a matching content identifier exists. As discussed above, each of the plurality of content identifiers (namely abalabz, alazcha, abalabz, alazcha) included within content directory  250  is associated with a piece of content previously-written to first cache system  126 . 
     If, when performing comparison  456 , data caching process  10  does not identify a content identifier included within content directory  250  that matches content identifier  138 , data caching process  10  may obtain  458  the previously-written content identified in read request  120  (i.e., content  132 ) from data array  130  and may write  460  content  132  to first cache system  126  (at e.g., first cache address 111011). Additionally, data caching process  10  may modify  462  content directory  250  to include a new entry (i.e., entry  262 ) that defines content identifier  138  (namely ablcboa), the location of content  132  within first cache system  126  (i.e., first cache address 111011), and the location of content  132  within data array  130  (i.e., LUN 6 /LBA 4 ). 
     If, when performing comparison  456 , data caching process  10  identifies a content identifier (either abalabz, alazcha, abalabz or alazcha) included within content directory  250  that matches content identifier  138 , data caching process  10  may retrieve  464  content  132  identified in read request  120  from first cache system  126 . 
     Further, data caching process  10  may also modify  466  an entry within content directory  250  that is associated with the matching content identifier to include a storage address that defines the storage location of content  132  (i.e., LUN 6 /LBA 4  within data array  130 ). This modification of a data entry within content directory  250  would be similar to the manner in which entry  260  was modified to create modified entry  260 ′. 
     For example, assume that the matching content identifier was again alazcha which was included within entry  260 . Accordingly, entry  260  would be modified to also identify the content stored at LUN 6 /LBA 4  (i.e., content  132 ) in addition to the content stored at LUN 4 /LBA 7 , as the content at LUN 6 /LBA 4  and LUN 4 /LBA 7  within data array  130  are identical. Accordingly, a single piece of cached content within first cache system  126  may be used as a local cached copy for both pieces of content stored on data array  130 . 
     Content Identifier Generation 
     Data caching process  10  may be configured to conserve storage space on data array  130  by deleting redundant data. 
     Referring also to  FIG. 10 , data caching process  10  may be configured to receive  500  read request  120  on first cache system  126 , wherein read request  120  identifies previously-written content (e.g., content  132 ) included within data array  130 . Upon receiving  450  read request  120 , data caching process  10  may process read request  120  to determine if content  132  is locally available within first cache system  126 . 
     As discussed above, read request  120  may define a particular logical unit within data array  130  (e.g., a LUN or Logical Unit Number) and a particular storage address within that specific logical unit (e.g., an LBA or Logical Block Address) for retrieving content  132  sought from data array  130 . 
     As discussed above, content directory  250  may include plurality of entries  252 , wherein each of these entries may identify: data array storage address  200 / 202  (e.g. a logical storage unit and a storage address at which a specific piece of previously-written content is located within storage array  130 ); first cache address  254  (e.g., the location within first cache system  126  at which the specific piece of previously-written content is also located), and content identifier  256  for the specific piece of previously-written content. 
     Accordingly, when data caching process  10  processes read request  120  to determine if content  132  is available within first cache system  126 , data caching process may review content directory  250  to see if the LUN and LBA defined within read request  120  is listed within content directory  250 . 
     Assume again for illustrative purposes that read request  120  is requesting the data stored at LUN 6 /LBA 4  of data array  130 . As LUN 6 /LBA 4  is not listed as a data array storage address  200 / 202  within content directory  250 , data caching process  10  will determine that the content requested in read request  120  is not available locally (i.e. from first cache system  126 ). 
     Accordingly, data caching process  10  may need to obtain  502  content  132  identified in read request  120  from data array  130 . In this particular example, since LUN 6 /LBA 4  is not defined within content directory  250 , a local cached copy of content  132  is not present/available within first cache system  126  and data caching process  10  will need to obtain  502  content  132  from data array  130 . 
     Once content  132  is obtained  502  from data array  130 , data caching process  10  may generate  504  a content identifier (e.g., content identifier  138 ) for content  132 . As discussed above, content identifier  138  generated  504  for the content  132  identified within read request  120  may be a hash function of content  132 . Assume for illustrative purposes that data caching process  10  generates a hash of content  132 , resulting in the generation  504  of content identifier  138  (namely hash value ablcboa). 
     Data caching process  10  may compare  506  content identifier  138  (i.e., the content identifier associated with the content identified within read request  120 , namely content  132 ) to each of the content identifiers (e.g., abalabz, alazcha, abalabz, alazcha) included within content directory  250  for first cache system  126  to determine if a matching content identifier exists. As discussed above, each of the plurality of content identifiers (namely abalabz, alazcha, abalabz, alazcha) included within content directory  250  is associated with a piece of content previously-written to first cache system  126 . 
     If, when performing comparison  506 , data caching process  10  does not identify a content identifier included within content directory  250  that matches content identifier  138 , data caching process  10  may write  508  content  132  to first cache system  126  (at e.g., first cache address 111011). Additionally, data caching process  10  may modify  510  content directory  250  to include a new entry (i.e., entry  262 ) that defines content identifier  138  (namely ablcboa), the location of content  132  within first cache system  126  (i.e., first cache address 111011), and the location of content  132  within data array  130  (i.e., LUN 6 /LBA 4 ). 
     If, when performing comparison  456 , data caching process  10  identifies a content identifier (either abalabz, alazcha, abalabz or alazcha) included within content directory  250  that matches content identifier  138 , data caching process  10  may modify  512  an entry within content directory  250  that is associated with the matching content identifier to include a storage address that defines the storage location of content  132  (i.e., LUN 6 /LBA 4  within data array  130 ). This modification of a data entry within content directory  250  would be similar to the manner in which entry  260  was modified to create modified entry  260 ′. 
     Assume for illustrative purposes that data caching process  10  generates a hash of content  132 , resulting in the generation  504  of content identifier  138  having a hash value of ablcboa. As the matching content identifier is included within entry  260  of content directory  250 , entry  260  may be modified  512  by data caching process  10  to also identify the piece of content stored at LUN 6 /LBA 4  (i.e., content  132 ) in addition to the piece of content stored at LUN 4 /LBA 7 , as the content at LUN 6 /LBA 4  and LUN 4 /LBA 7  within data array  130  are identical. 
     Additionally, if a matching content identifier is identified, data caching process  10  may notify  514  data array  130  that content  130  identified in read request  120  is identical to the previously-written content associated with the matching content identifier. Accordingly and in this example, content  130  stored at LUN 6 /LBA 4  within data array  130  is identical to the content stored at LUN 4 /LBA 7  within data array  130 . Once notified  516 , data array  130  may e.g., delete one of the redundant copies (e.g., at LUN 6 /LBA 4  or LUN 4 /LBA 7 ) on e.g., non-volatile, electro-mechanical memory system  112  and/or second cache system  128  and may map LUN 6 /LBA 4  and LUN 4 /LBA 7  to a single memory location within e.g., non-volatile, electro-mechanical memory system  112  and/or second cache system  128 . 
     As will be appreciated by one skilled in the art, the present disclosure may be embodied as a method, system, or computer program product. Accordingly, the present disclosure may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a “circuit,” “module” or “system.” Furthermore, the present disclosure may take the form of a computer program product on a computer-usable storage medium having computer-usable program code embodied in the medium. 
     The flowchart and block diagrams in the Figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods and computer program products according to various embodiments of the present disclosure. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and computer instructions. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present disclosure has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the disclosure in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the disclosure. The embodiment was chosen and described in order to best explain the principles of the disclosure and the practical application, and to enable others of ordinary skill in the art to understand the disclosure for various embodiments with various modifications as are suited to the particular use contemplated. 
     A number of implementations have been described. Having thus described the disclosure of the present application in detail and by reference to embodiments thereof, it will be apparent that modifications and variations are possible without departing from the scope of the disclosure defined in the appended claims.