Abstract:
In one embodiment, a storage system comprises: a first type interface being operable to communicate with a server using a remote memory access; a second type interface being operable to communicate with the server using a block I/O (Input/Output) access; a memory; and a controller being operable to manage (1) a first portion of storage areas of the memory to allocate for storing data, which is to be stored in a physical address space managed by an operating system on the server and which is sent from the server via the first type interface, and (2) a second portion of the storage areas of the memory to allocate for caching data, which is sent from the server to a logical volume of the storage system via the second type interface and which is to be stored in a storage device of the storage system corresponding to the logical volume.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to storage systems and, more particularly, to hierarchy memory management between server and storage system using RDMA (Remote Direct Memory Access) technology. 
     Remote memory access and allocation technology such as RDMA (Remote Direct Memory Access) is available. One approach involves dynamic memory management in an RDMA context (see, e.g., U.S. Pat. No. 7,849,272). Another approach involves distributed shared memory on a plurality of computers (see, e.g., US2009/0144388). Server attached PCI-Express™ flash is cheaper bit cost than large capacity RDIMM (Registered Dual Inline Memory Module) module. 
     A server has limited physical memory capacity which depends on the CPU architecture. To expand the capacity of Server DRAM (Direct Random Access Memory), RDIMM (Registered Dual Inline Memory Module) is required. Large capacity RDIMM is highest cost of any other DIMM type. Server DIMM socket is not hot swappable. To expand the memory capacity of the server, the server administrator stops the OS (Operation System) and stops power to the server, and then the server administrator installs DIMM to DIMM slot of the motherboard. 
     Local server memory provides higher performance than remote memory access by RDMA (Remote Direct Memory Access), since DDR SDRAM (Double-Data-Rate Synchronous Dynamic Random Access Memory) interface has higher access latency and capacity of network throughput than RDMA network. DRAM has lower access latency than flash memory. Conventional technology does not disclose (1) which type of local memory or remote memory is better hierarchy for performance and (2) which type of DRAM, flash memory, or other new memory device has the best hierarchy of DRAM memory tier. Also, current memory allocation of RDMA protocol does not provide memory type information. 
     Cache memory of storage system constitutes DRAM and/or flash memory. Current storage system does not share memory of storage system as both of storage cache and server memory expansion. 
     BRIEF SUMMARY OF THE INVENTION 
     Exemplary embodiments of the invention provide a server that manages local and remote memory and hierarchy. A storage manages a server allocation memory region. The storage manages partitioning of DRAM or Flash memory between storage cache data area and server memory data. Both the server and the storage have remote memory interface and storage block I/O interface. The server has remote hierarchy cache management to allocate or de-allocate local or remote physical address space. The storage manages to allocate cache data area and server memory data. As such, the server manages the hierarchy memory and it is easier to expand the server memory area without the host OS (Operating System) stopping. Furthermore, the storage provides memory space as server memory data and consolidates server memory resources to physical memory pool of multiple storages. 
     In accordance with an aspect of the present invention, a storage system comprises: a first type interface being operable to communicate with a server using a remote memory access; a second type interface being operable to communicate with the server using a block I/O (Input/Output) access; a memory; and a controller being operable to manage (1) a first portion of storage areas of the memory to allocate for storing data, which is to be stored in a physical address space managed by an operating system on the server and which is sent from the server via the first type interface, and (2) a second portion of the storage areas of the memory to allocate for caching data, which is sent from the server to a logical volume of the storage system via the second type interface and which is to be stored in a storage device of the storage system corresponding to the logical volume. 
     In some embodiments, the controller is operable to manage capacity information for each media type of the memory in the storage system. The memory includes at least one of DRAM memory or Flash memory. The controller is operable to manage (3) a third portion of storage areas of the memory to allocate for storing data, which is to be stored in a physical address space managed by an operating system on another server and which is sent from said another server via the first type interface, and to manage the second portion of the storage areas of the memory to allocate for caching data, which is sent from said another server to a logical volume of the storage system via the second type interface and which is to be stored in a storage device of the storage system corresponding to the logical volume. The controller is operable to provide, to the server in response to a request from the server, capacity information for each media type of the first portion of storage areas of the memory in the storage system. 
     In specific embodiments, the controller is operable, if a remote memory interface of the server for communicating with the first type interface is stopped, to remove the server from an entry of a server memory allocate table which stores information on allocated memory by the storage system for one or more servers. The controller is operable, in response to a remote memory binding request with one of required capacity and memory performance or memory assign location range of the first portion of storage areas of the memory from the server, to return memory binding result with mapped address information to the server. The controller is operable, in response to a remote free request from the server, to remove the server from an entry of a server memory allocate table which stores information on allocated memory by the storage system for one or more servers. 
     Another aspect of the invention is directed to a method of memory management for a storage system having a first type interface being operable to communicate with a server using a remote memory access, a second type interface being operable to communicate with the server using a block I/O (Input/Output) access, and a memory. The method comprises managing (1) a first portion of storage areas of the memory to allocate for storing data, which is to be stored in a physical address space managed by an operating system on the server and which is sent from the server via the first type interface, and (2) a second portion of the storage areas of the memory to allocate for caching data, which is sent from the server to a logical volume of the storage system via the second type interface and which is to be stored in a storage device of the storage system corresponding to the logical volume. 
     In some embodiments, the method further comprises removing the server from an entry of a server memory allocate table which stores information on allocated memory by the storage system for one or more servers, if a remote memory interface of the server for communicating with the first type interface is stopped or if a remote free request is received from the server. 
     Another aspect of this invention is directed to a computer-readable storage medium storing a plurality of instructions for controlling a data processor to manage memory for a storage system having a first type interface being operable to communicate with a server using a remote memory access, a second type interface being operable to communicate with the server using a block I/O (Input/Output) access, and a memory. The plurality of instructions comprise instructions that cause the data processor to manage (1) a first portion of storage areas of the memory to allocate for storing data, which is to be stored in a physical address space managed by an operating system on the server and which is sent from the server via the first type interface, and (2) a second portion of the storage areas of the memory to allocate for caching data, which is sent from the server to a logical volume of the storage system via the second type interface and which is to be stored in a storage device of the storage system corresponding to the logical volume. 
     In some embodiments, the plurality of instructions further comprise instructions that cause the data processor to manage capacity information for each media type of the memory in the storage system, wherein the memory includes at least one of DRAM memory or Flash memory. The plurality of instructions further comprise instructions that cause the data processor, if a remote memory interface of the server for communicating with the first type interface is stopped, to remove the server from an entry of a server memory allocate table which stores information on allocated memory by the storage system for one or more servers. The plurality of instructions further comprise instructions that cause the data processor, in response to a remote memory binding request with one of required capacity and memory performance or memory assign location range of the first portion of storage areas of the memory from the server, to return memory binding result with mapped address information to the server. The plurality of instructions further comprise instructions that cause the data processor, in response to a remote free request from the server, to remove the server from an entry of a server memory allocate table which stores information on allocated memory by the storage system for one or more servers. 
     These and other features and advantages of the present invention will become apparent to those of ordinary skill in the art in view of the following detailed description of the specific embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an Example of a hardware configuration of a system in which the method and apparatus of the invention may be applied. 
         FIG. 2  shows an example of memory address mapping for the configuration of  FIG. 1 . 
         FIG. 3  shows an example of a detailed configuration of the system of  FIG. 1 . 
         FIG. 4  shows an example of memory partition in the storage system. 
         FIG. 5  shows an example of memory address mapping for DRAM and Flash memory hierarchy and remote access for the configuration of  FIGS. 3 and 4 . 
         FIG. 6  shows an example of a hardware configuration of a system having multiple storage systems. 
         FIG. 7  shows an example of memory address mapping for DRAM and Flash memory hierarchy and remote access for the configuration of  FIG. 6 . 
         FIG. 8  shows an example of a hardware configuration of a system having multiple servers and multiple storage systems. 
         FIG. 9  shows an example of memory address mapping for DRAM and Flash memory hierarchy and remote access for the configuration of  FIG. 8 . 
         FIG. 10  shows an example of the device discovery table in the host server. 
         FIG. 11  shows an example of the address mapping table in the host server. 
         FIG. 12  shows an example of the memory partition table in the storage. 
         FIG. 13  shows an example of the server memory allocate table in the storage. 
         FIG. 14  is an example of a flow diagram illustrating a process flow of the memory device discovery and initialization process. 
         FIG. 15  is an example of a flow diagram illustrating a process flow of the memory device discovery and initialization process. 
         FIG. 16  is an example of a flow diagram illustrating a process flow of server memory allocation. 
         FIG. 17  is an example of a flow diagram illustrating a process flow of server memory de-allocation (free) system call. 
         FIG. 18  is an example of a flow diagram illustrating a memory read operation. 
         FIG. 19  is an example of a flow diagram illustrating a memory write operation. 
         FIG. 20  is an example of a flow diagram illustrating a block I/O write operation. 
         FIG. 21  is an example of a flow diagram illustrating a block I/O read operation. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following detailed description of the invention, reference is made to the accompanying drawings which form a part of the disclosure, and in which are shown by way of illustration, and not of limitation, exemplary embodiments by which the invention may be practiced. In the drawings, like numerals describe substantially similar components throughout the several views. Further, it should be noted that while the detailed description provides various exemplary embodiments, as described below and as illustrated in the drawings, the present invention is not limited to the embodiments described and illustrated herein, but can extend to other embodiments, as would be known or as would become known to those skilled in the art. Reference in the specification to “one embodiment,” “this embodiment,” or “these embodiments” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention, and the appearances of these phrases in various places in the specification are not necessarily all referring to the same embodiment. Additionally, in the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to one of ordinary skill in the art that these specific details may not all be needed to practice the present invention. In other circumstances, well-known structures, materials, circuits, processes and interfaces have not been described in detail, and/or may be illustrated in block diagram form, so as to not unnecessarily obscure the present invention. 
     Furthermore, some portions of the detailed description that follow are presented in terms of algorithms and symbolic representations of operations within a computer. These algorithmic descriptions and symbolic representations are the means used by those skilled in the data processing arts to most effectively convey the essence of their innovations to others skilled in the art. An algorithm is a series of defined steps leading to a desired end state or result. In the present invention, the steps carried out require physical manipulations of tangible quantities for achieving a tangible result. Usually, though not necessarily, these quantities take the form of electrical or magnetic signals or instructions capable of being stored, transferred, combined, compared, and otherwise manipulated. It has proven convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers, instructions, or the like. It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise, as apparent from the following discussion, it is appreciated that throughout the description, discussions utilizing terms such as “processing,” “computing,” “calculating,” “determining,” “displaying,” or the like, can include the actions and processes of a computer system or other information processing device that manipulates and transforms data represented as physical (electronic) quantities within the computer system&#39;s registers and memories into other data similarly represented as physical quantities within the computer system&#39;s memories or registers or other information storage, transmission or display devices. 
     The present invention also relates to an apparatus for performing the operations herein. This apparatus may be specially constructed for the required purposes, or it may include one or more general-purpose computers selectively activated or reconfigured by one or more computer programs. Such computer programs may be stored in a computer-readable storage medium including non-transient medium, such as, but not limited to optical disks, magnetic disks, read-only memories, random access memories, solid state devices and drives, or any other types of media suitable for storing electronic information. The algorithms and displays presented herein are not inherently related to any particular computer or other apparatus. Various general-purpose systems may be used with programs and modules in accordance with the teachings herein, or it may prove convenient to construct a more specialized apparatus to perform desired method steps. In addition, the present invention is not described with reference to any particular programming language. It will be appreciated that a variety of programming languages may be used to implement the teachings of the invention as described herein. The instructions of the programming language(s) may be executed by one or more processing devices, e.g., central processing units (CPUs), processors, or controllers. 
     Exemplary embodiments of the invention, as will be described in greater detail below, provide apparatuses, methods and computer programs for hierarchy memory management between server and storage system using RDMA technology. 
       FIG. 1  illustrates an example of a hardware configuration of a system in which the method and apparatus of the invention may be applied. The system represents a computer environment having a host server  1  and a storage  2 . The server  1  and storage  2  are connected by block I/O interface  13  such as SCSI (small computer system interface). The host server  1  has a DRAM memory  11  for storing server memory data and a processor  12 . 
       FIG. 2  shows an example of memory address mapping for the configuration of  FIG. 1 . The server OS (Operation System) has virtual memory address space  200 . The server OS manages to map OS between the virtual memory address space  200  and the DRAM physical address space  210 . When the server OS allocates memory in the virtual memory address, the allocator program of the server OS gathers some segments of the physical address space  210  and maps them to one contiguous server memory data segment. The server memory data  40  is one contiguous memory segment in the virtual address space  200 . The allocation data  41  is the actual memory segment of the server memory data  40  in the physical address space  210 . The server memory data  40  is mapped to one or multiple segments of the allocation data  41 . 
       FIG. 3  shows an example of a detailed configuration of the system of  FIG. 1 . The host server  1  includes processor  12 , DRAM memory  11  for server memory data, Flash memory  14  for server memory data, and address mapping table  16  for management of local and remote hierarchy memory address space. The host server  1  has remote memory interface  15  for access remote hierarchy memory address space, and block I/O interface  13  for access data store in the storage  2 . The storage  2  includes processor  22 , data store  28 , DRAM memory  21  for hierarchy memory space and cache memory of the storage data store  28 , Flash memory  24  for hierarchy memory space and cache memory of the storage data store  28 , remote memory interface  25 , block I/O interface  23 , memory partition table  26  for partitioning DRAM/Flash memory of the storage  2  to area of server storage data and area of storage cache memory, and server memory allocate table  27 . 
       FIG. 4  shows an example of memory partition in the storage system. The storage system  2  has a large capacity of DRAM memory  21  and Flash memory  24 . The memory partition table  26  manages to divide the storage cache memory area  110  for storage block access data caching and server memory data area  100  for server physical memory address space. 
       FIG. 5  shows an example of memory address mapping for DRAM and Flash memory hierarchy and remote access for the configuration of  FIGS. 3 and 4 . When the host allocates the server memory data  40  in the logical memory address space (OS virtual address space), the host OS maps to the local DRAM or PRAM memory address space  210 , remote DRAM or PRAM address space  220 , local flash address space  230 , or remote flash address space  240 . When the host server  1  allocates the server memory data  40 , the host OS issues a memory allocation system call based on the required highest access frequency to the local DRAM memory  21 . When the host OS or application does not require highest performance for memory access, the host OS allocates the server memory data area to Flash memory  24  or remote DRAM address space  220  or remote Flash memory address space  240 . The host OS manages the address mapping table  16  to allocate region of the physical memory address space ( 210 - 240 ). 
       FIG. 6  shows an example of a hardware configuration of a system having multiple storage systems. In this computer environment, the server  1  has the same composition as that in  FIG. 3  and each storage  2  has the same composition as that in  FIG. 3 . This embodiment involving multiple storage systems creates a “distributed physical address space”  50  of server memory data using storage DRAM memory  21  and storage Flash memory  24 . The distributed physical address space  50  is separated from the storage cache memory space in each of the multiple storage systems  2 . 
       FIG. 7  shows an example of memory address mapping for DRAM and Flash memory hierarchy and remote access for the configuration of  FIG. 6 . The physical memory address space  220  of remote DRAM address space and the physical memory address space  240  of remote Flash address space are shared by logical memory address  200  of the host  40 . There are one logical memory addresses # 1   200 , separate remote DRAM address spaces  220   a ,  220   b , and separate remote Flash address spaces  240   a ,  240   b.    
       FIG. 8  shows an example of a hardware configuration of a system having multiple servers and multiple storage systems. In this computer environment, the multiple servers  1  share the distributed physical address space  50  as a server memory capacity pool. 
       FIG. 9  shows an example of memory address mapping for DRAM and Flash memory hierarchy and remote access for the configuration of  FIG. 8 . The physical memory address space  220  of remote DRAM address space and the physical memory address space  240  of remote Flash address space are shared by multiple logical memory addresses  200   a  and  200   b  of the two hosts. There are separate logical memory addresses # 1   200   a  and # 2   200   b , separate local DRAM address spaces  210   a ,  210   b , and separate local Flash address spaces  230   a ,  230   b.    
       FIG. 10  shows an example of the device discovery table  17  in the host server  1 . Remote Device field  91  is local address (local RAM or Flash memory) or identification of remote memory device such as Inifiniband® name identifier. Memory Device Type field  92  contains media type of memory such as DRAM, PRAM, or Flash. Assigned capacity field  93  contains local or remote assigned capacity that is allocated by server of physical memory address space. 
       FIG. 11  shows an example of the address mapping table  16  in the host server  1 . Virtual memory address field  101  is address space of host OS virtual address space  200 . Remote Device field  102  is local address (local RAM or Flash memory) or identification of remote memory device such as Inifiniband® name identifier. Memory Device Type field  103  contains media type of memory such as DRAM, PRAM, or Flash. Physical Memory address field  104  contains local or remote physical memory address. 
       FIG. 12  shows an example of the memory partition table  26  in the storage  2 . The memory partition table  26  divides DRAM memory or Flash memory of storage to server memory data area and storage cache data area. Physical Memory address field  111  contains physical memory address of the storage Flash or storage DRAM memory. Memory Device Type field  112  contains media type of memory such as DRAM, PRAM, or Flash. Partition Type field  113  contains memory area type of storage cache memory area or server memory data area. Remote Device field  114  contains identification of remote host server such as Inifiniband® name identifier. 
       FIG. 13  shows an example of the server memory allocate table  27  in the storage  2 . The server memory allocate table  27  enables to share physical address space of server memory data amongst multiple servers. Remote Device field  121  contains identification of remote host server such as Inifiniband® name identifier. Memory Device Type field  122  contains local resource media type of memory such as DRAM, PRAM, or Flash. Physical Memory address field  123  contains local physical memory address. 
       FIG. 14  is an example of a flow diagram illustrating a process flow of the memory device discovery and initialization process. When the network  51  detects a new server or storage device, the network  51  notifies all devices. Then the host server  1  discovers a new storage device  2  that has remote memory device capability (step S 131 ). The host server  1  adds the remote memory device resource to the remote device entry  91  of the device discovery table  17  ( FIG. 10 ). In step S 132 , the host server  1  gets the capacity information for each media type for each new discovery remote memory device, and constructs the memory type entry  92  and assigned capacity entry  93  of the device discovery table  17 . In step S 136 , the storage  2  returns capacity information to the reference memory partition table  26 . The memory partition table contains available capacity of remote physical memory that the host uses to remote physical memory. In S 136 , the storage returns capacity information of the remote physical memory. In step S 133 , the host server  1  determines which host server has enough memory capacity or memory performance. If the capacity or performance is enough (YES), the program skips step S 134  and proceeds to step S 135 . Otherwise, the program performs step S 134 , in which the host server  1  requests more capacity allocation to a specific memory type. When the storage  2  receives the request, the storage  2  returns good result with memory type and allocation capacity. If the storage  2  does not have more resources to allocate any capacity to the host server, then the storage returns a bad status with a lack of capacity error. In step S 135 , the host OS updates the memory capacity. The host OS dynamically updates the physical capacity without OS reboot or shutdown process. 
       FIG. 15  is an example of a flow diagram illustrating a process flow of the memory device discovery and initialization process. In step S 141 , the administrator stops the server OS or the application program running the host serve  1  issues a free memory call. In step S 142 , the storage  2  de-allocates the memory corresponding to the host server. In step S 143 , if the remote memory interface of the host server  1  is stopped, the storage  2  removes entry of the specific server device (Remote Device) entry of the server memory allocate table  27  ( FIG. 13 ). 
       FIG. 16  is an example of a flow diagram illustrating a process flow of server memory allocation (alloc). In step S 151 , the host OS requests new server memory data. The application of the host  1  issues a memory allocation system call to the host OS. In step S 152 , if the local memory of the host server has sufficient capacity (YES), then the host OS allocates local memory and proceeds to step S 156 . If the local memory of the host server does not have sufficient capacity or the higher performance memory capacity such as DRAM is insufficient (NO), then the program performs steps S 153  to S 155  before step S 156 . 
     In step S 153 , the host server  1  checks the remote memory capacity using the device discovery table  17 . If remote memory is available (YES), then the next step is S 154 . If remote memory is not available (NO), then memory allocation has failed and the host OS requires a swap operation to expand capacity of total memory. The swap operation is virtual memory address map to memory data move to file block and store to data store of block storage. In step S 154 , the host memory issues a remote memory binding request such as RDMA operation memory allocation functionality to the storage memory interface. The host requests memory binding with required capacity and memory performance or memory assign location range of remote DRAM area or remote Flash area. In step S 155 , the storage  2  updates the server memory allocation table  27  and returns physical memory of remote DRAM or Flash address space which host requests specific performance or remote memory address space. The storage returns memory binding result with mapped address information. In step S 156 , the host OS updates the address mapping table  16  to allocate local or remote memory. Application is used to access the server memory data that is mapped to local memory area, or remote memory area using RDMA. 
       FIG. 17  is an example of a flow diagram illustrating a process flow of server memory de-allocation (free) system call. In step S 161 , the host OS requests to free server memory data. Application of the host  1  issues a memory de-allocation (memory free) system call to the host OS. In step S 162 , if the allocation area is local memory of the host server (YES), then the host OS de-allocates the local memory and proceeds to step S 166 . If the allocation area is remote memory (NO), then the program performs steps S 163  to S 165  before steps S 166 . 
     In step S 163 , the host memory issues a remote memory free request to the remote memory interface  25  of the storage  2 . In step S 164 , the storage  2  checks the remote memory capacity using the device discovery table  17 . If the remote memory is allocated (YES), then the next step is S 165 . If the remote memory is not allocated (NO), then the memory free request has failed due to memory address violation. The remote memory interface  25  of the storage  2  returns result with memory violation error response, and then the host OS performs memory error handling. In step S 165 , the storage  2  updates the server memory allocation table  27  to remove specific entry and return result of memory free request. In step S 166 , the host OS updates the address mapping table  16  to remove specific remote memory allocation entry, and then to de-allocate local or remote memory. The virtual memory address space of host server cleanup server memory data. 
       FIG. 18  is an example of a flow diagram illustrating a memory read operation. The host  1  issues a memory read operation to the storage  2 . The storage checks the server memory allocate table  27  for the allocated physical address  123 , sends the read data from the server memory data area  100  to the host, and returns result of the memory read operation to the host. The data transfer from the storage to the host occurs when the storage sends the read data from the server memory data area  100  to the host. 
       FIG. 19  is an example of a flow diagram illustrating a memory write operation. The host  1  issues a memory write operation to the storage  2 . The storage checks the server memory allocate table  27  for the allocated physical address  123 , reads data from the host to the server memory data area  100  of the storage, and returns result of the memory write operation to the host. The data transfer from the storage to the host and back to the storage occurs when the storage reads data from the host to the server memory data area  100  of the storage. This flow is for “server write memory data in the server local memory to remote memory.” The server issues a memory write command to the storage via the RDMA interface. In the next step, the storage receives the RDMA memory write command. The storage checks the server memory allocate table  27  for the allocated physical address  123 . Then, the storage gets (read) write data which has already existed in the server local memory (host write data). The RDMA data transfer operation is initiated by the target. The host sends write memory data to the storage. The storage performs the RDMA write operation to read the host local memory data. 
       FIG. 20  is an example of a flow diagram illustrating a block I/O write operation. The host  1  issues a block I/O write operation to the storage  2 . The storage checks the memory partition table  26  for the partition type  113  (storage cache) and the physical memory address  111 , and notifies the host  1  when it is ready for data transfer. In response, the host sends write data to the storage. The storage stores the write data to the storage cache area  110 , returns result of the block I/O write operation to the host, and destages dirty data from the storage cache area  110  to the data store  28 . The data transfer from the host to the storage occurs when the host sends the write data to the storage. 
       FIG. 21  is an example of a flow diagram illustrating a block I/O read operation. The host  1  issues a block I/O read operation to the storage  2 . The storage checks the memory partition table  26  for the partition type  113  (storage cache) and the physical memory address  111 , performs staging of read data from the data store  28  to the cache memory area  110 , sends block read I/O data to the host, and returns result of the block I/O read operation to the host. The data transfer occurs from the storage to the host when the storage returns block read I/O data to the host. 
     Of course, the system configurations illustrated in  FIGS. 1, 6 , and  7  are purely exemplary of information systems in which the present invention may be implemented, and the invention is not limited to a particular hardware configuration. The computers and storage systems implementing the invention can also have known I/O devices (e.g., CD and DVD drives, floppy disk drives, hard drives, etc.) which can store and read the modules, programs and data structures used to implement the above-described invention. These modules, programs and data structures can be encoded on such computer-readable media. For example, the data structures of the invention can be stored on computer-readable media independently of one or more computer-readable media on which reside the programs used in the invention. The components of the system can be interconnected by any form or medium of digital data communication, e.g., a communication network. Examples of communication networks include local area networks, wide area networks, e.g., the Internet, wireless networks, storage area networks, and the like. 
     In the description, numerous details are set forth for purposes of explanation in order to provide a thorough understanding of the present invention. However, it will be apparent to one skilled in the art that not all of these specific details are required in order to practice the present invention. It is also noted that the invention may be described as a process, which is usually depicted as a flowchart, a flow diagram, a structure diagram, or a block diagram. Although a flowchart may describe the operations as a sequential process, many of the operations can be performed in parallel or concurrently. In addition, the order of the operations may be re-arranged. 
     As is known in the art, the operations described above can be performed by hardware, software, or some combination of software and hardware. Various aspects of embodiments of the invention may be implemented using circuits and logic devices (hardware), while other aspects may be implemented using instructions stored on a machine-readable medium (software), which if executed by a processor, would cause the processor to perform a method to carry out embodiments of the invention. Furthermore, some embodiments of the invention may be performed solely in hardware, whereas other embodiments may be performed solely in software. Moreover, the various functions described can be performed in a single unit, or can be spread across a number of components in any number of ways. When performed by software, the methods may be executed by a processor, such as a general purpose computer, based on instructions stored on a computer-readable medium. If desired, the instructions can be stored on the medium in a compressed and/or encrypted format. 
     From the foregoing, it will be apparent that the invention provides methods, apparatuses and programs stored on computer readable media for hierarchy memory management between server and storage system using RDMA technology. Additionally, while specific embodiments have been illustrated and described in this specification, those of ordinary skill in the art appreciate that any arrangement that is calculated to achieve the same purpose may be substituted for the specific embodiments disclosed. This disclosure is intended to cover any and all adaptations or variations of the present invention, and it is to be understood that the terms used in the following claims should not be construed to limit the invention to the specific embodiments disclosed in the specification. Rather, the scope of the invention is to be determined entirely by the following claims, which are to be construed in accordance with the established doctrines of claim interpretation, along with the full range of equivalents to which such claims are entitled.