Abstract:
A storage subsystem that directly interfaces with a network, provides connections for routers with a conventional multi-path function, and performs access load balancing among a plurality of input/output ports. Each channel controller is assigned with a channel controller network address, and a storage device is assigned with a storage device address (different from the network addresses of the channel controllers). Upon receiving a packet addressed to the storage device address from an external network device, a pseudo storage load routing function responds by notifying the external network device that the packet has been transmitted to the storage device with the storage device address, while performing input/output processing indicated by the packet for the storage device with the storage device address.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a storage subsystem, more particularly to a storage subsystem providing interfaces with an external network through a plurality of input/output ports and connectable to existing routers and other equipment without requiring any alterations at the external end thereof, that expands processing capability by distributing network packet traffic among the input/output ports so as to avoid load concentration. 
     2. Description of Related Art 
     In recent years, the explosive proliferation of the Internet and the emergence of gigabit Ethernet are enhancing network infrastructure, speed, and bandwidth. In addition, since a network using the Internet Protocol (IP) (“an IP network” hereinafter) has the advantages of low management and operating costs and higher interconnectivity than typically seen in Local Area Networks (LANs), the concept of a Storage Area Network (SAN) has emerged. A SAN refers to a network environment for storage-only devices, in which one or more host computers and one or more storage devices are linked together. The storage devices may include a disk array subsystem (hereinafter “a storage subsystem”). 
     The typical structure of a storage subsystem is described below with reference to FIG.  7 . 
     FIG. 7 is a block diagram of a typical storage subsystem. 
     The storage subsystem  100  comprises a channel controller  105 , a disk access controller  120 , a coupled unit  110 , and a storage device  130 , and the coupled unit  110  includes a memory controller  140 . 
     The channel controller  105  receives an access request from a host computer, analyzes the access request and performs other processing. The disk access controller  120  controls the channel controller  105 &#39;s access to the storage device  130 . 
     The coupled unit  110  provides coupling between the channel controller  105  and the disk access controller  120 . The memory controller  140  stores the control information about data transmission between the channel controller  105  and the disk access controller  120 , and stores data that a host computer reads from and writes to the storage device  130 . 
     The storage device  130  comprises hard disk devices that store a large amount of data. 
     As the network speed and bandwidth increase, increasing access requests from host computers arrive, which places mounting loads on the storage device. Due to this background, technology for balancing storage device loads has been proposed. For example, JP-A-330924/2000 discloses a method for a host computer side to detect routes of access to a target storage device, and to balance the load on the storage device among the routes of access. 
     However, the prior art described above balances load by having the host computer provide a unique number identifying the target storage device. Therefore, there is a problem in that the host computer requires an additional means for providing unique numbers for storage devices so as to lack expandability. 
     In general, servers and other equipment on an Ethernet network have network addresses known as Internet Protocol (IP) addresses and Media Access Control (MAC) addresses, so they do not require the additional means mentioned above. A router distributes the access load with these network addresses. Typical functions of a router include a routing function by which a route of transmission to a destination IP network address is found. Protocols supporting the routing function include the Route Information Protocol (RIP), and the Open Shortest Path First (OSPF). 
     Extensions of the routing function using protocols, such as RIP and OSPF, includes a function (“a multi-path function” hereinafter) for performing load balancing among a plurality of routes of transmission to a destination IP address thereby using alternative routes when a failure occurs on one of the routes. 
     The multi-path function is described briefly with reference to FIG.  8  and FIG.  9 . 
     FIG. 8 is a drawing showing an example of a network structure having a plurality of network relay routes. 
     FIG. 9 is a drawing showing routing tables and a table of information of a multi-path of a router. 
     In the network structure shown in FIG. 8, routes of access from a relay router  201  in a network  220  to a server  210  within a local site  230  include three routes of relay between networks  205 ,  206 , and  207 . 
     Within the local site  230 , since there is an edge router  208  with only one route to the server  210 , the question in this case concerns the routes between the relay router  201  and the edge router  208 . 
     In the example shown in FIG. 8, since there are three routes of access between the relay router  201  and the edge router  208 , the server  210  can be accessed through any of the routes of relay between networks  205 ,  206 , and  207 . 
     In order to describe the multi-path function, a routing table for a conventional routing function, shown in FIG.  9 ( a ), is described. The main elements of the routing table are a destination address  301  that gives a destination IP address, a subnet mask  302  that gives mask information for identifying the network including the address given by the destination address  301 , a next hop address  303  that gives the IP address of the next relay router, and an output interface  304  that indicates which output port in the router is linked to the next relay router. 
     FIG.  9 ( b ) shows a routing table used when there are a plurality of next hop routers, or a plurality of routes of access. In the routing table in FIG.  9 ( b ), although the destination address  301  and subnet mask  302  are the same as in FIG.  9 ( a ), a plurality of next hop addresses are registered as information of multi-path  310 . The information of multi-path  310  includes information about the routes concerned (route  1 , route  2 , and route  3 ) and the output interfaces (output interface A, output interface B, and output interface C) ( 311 ,  312 , and  313 ). If there are a plurality of routes to an address given by the destination address  301 , the output port is selected from the routes that have been registered in the information of multi-path  310 . The multi-path function accordingly implements access load balancing by using a plurality of routes of access without requiring additional means at the host computer. 
     However, there is a restriction that the multi-path function and routing protocols are applicable only when there are a plurality of routes of access to a single IP address. That is, even if there are a plurality of routes, the target network device must be treated as a single device. 
     If a storage subsystem having a plurality of input/output ports is used in an IP network, each of the input/output ports has an IP address and a MAC address. Therefore, a plurality of IP addresses and MAC addresses exist in the storage subsystem, presenting a problem that makes it impossible to use the multi-path function. 
     If the multi-path function is not used, users external to the network must communicate with the input/output ports by using their IP addresses and MAC addresses or must add additional equipment for load balancing. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a storage subsystem having a plurality of input/output ports, that enables access on the storage subsystem and to balance the load over the plurality of input/output ports without requiring additional means in the external network environment or a host computer, and to establish connections with networks easily using the functions of currently available network equipment. 
     To attain this object, the present invention implements load balancing and expands processing capability by making the channel controllers within a storage subsystem having a plurality of input/output ports behave as virtual routers on the routes to a virtual destination IP address, which is assigned to a storage device within the storage subsystem to take advantage of the conventional multi-path function of existing routers. Alternatively, the present invention assigns IP addresses to individual units (e.g. individual volumes or individual storage devices) to implement access load balancing within those individual units. Furthermore, the invention addresses requests for network bandwidth from customers with the storage subsystem, which is adopted to handle accessing peak times, by updating the address management tables of channel controllers. 
     This invention therefore provides a storage subsystem that balances access loads on the storage subsystem at the plurality of input/output ports without additional means in the external network environment or a host computer. At the same time, the storage subsystem interfaces with a network by using the functions of currently available network equipment. 
     Other and further objects, features and advantages of the invention will appear more fully from the following description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The preferred embodiments of the present invention are illustrated in the accompanying drawings in which: 
     FIG. 1 is a block diagram of a storage subsystem of a first embodiment of the present invention; 
     FIG. 2 is a block diagram of a channel controller; 
     FIG. 3 is a diagram of an address management table; 
     FIG. 4 is a conceptual diagram describing communication operations in the storage subsystem of the first embodiment of the invention; 
     FIG. 5 is a block diagram of a storage subsystem of a second embodiment of the invention; 
     FIG. 6 is a conceptual diagram for describing the communication operations in the storage subsystem of the second embodiment of the invention; 
     FIG. 7 is a block diagram of a general storage subsystem; 
     FIG. 8 is a drawing showing an example of a network structure having a plurality of network relay routes; and 
     FIG. 9 is a drawing showing routing tables and a table of information of multi-path in a router. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention are described below with reference to FIG. 1 to FIG. 6 
     First Embodiment 
     The first embodiment of the present invention is described with reference to FIG. 1 to FIG.  4 . 
     First, the structure of a storage subsystem according to the first embodiment of the present invention is described with reference to FIG.  1 . 
     FIG. 1 is a block diagram of the storage subsystem of the first embodiment of the invention. 
     The host computer  401  is connected to a network and sends access request packets to the storage subsystem  470 . The router  402  has a function of routing packets on the network and thereby couples the storage subsystem  470  and the host computer  401 . The path  415  between the host computer  401  and the router  402  may include another network. 
     The channel controllers  403  to  410  receive access request packets from the router, perform protocol processing, including packet analysis, and issue requests for access to the storage device  450  via the disk access controller  440 . The channel controllers  403  to  410  are assigned unique addresses  420  to  427  (AD 1 , AD 2 , AD 3 , AD 4 , AD 5 , AD 6 , AD 7 , and AD 8 ) respectively. Each channel controller address (AD) includes an IP address and a MAC address. For example, channel controller  406  is assigned IP 4  and MAC 4  as its unique address. 
     The coupled unit  430  is implemented by a crossbar switch or the like, and it has a mechanism for coupling each channel controller to the storage access controller  440 . Each channel controller can issue an access command to any storage access controllers  440  via the coupled unit  430 . 
     The memory controller  490  has a memory for storing access data from clients and control information about accesses between the channel controllers  403 - 410  and the storage access controllers  440 . 
     The storage access controller  440  controls access to the storage device  450 . The storage device  450  stores data from clients, and usually comprises large-capacity hard storage drives. 
     The storage device  450  is assigned with a storage device address AD-X. 
     The router  402  and the storage subsystem  470  are interconnected via paths  480  to  487  and exchange packets through the input/output ports of the channel controllers  403  to  410 . The example in FIG. 4 shows eight input/output ports, but the invention is not limited to any specific number of input/output ports. 
     The apparatus for establishing an address  495  may be an external console, which establishes addresses for the channel controllers  403  to  410  and the storage device  450 . 
     Next, the structure of a channel controller is described with reference to FIG.  2  and FIG.  3 . 
     FIG. 2 is a block diagram of a channel controller. 
     FIG. 3 is a diagram of an address management table. 
     Because each of the channel controllers  403  to  410  has the same structure, the structure is described with reference to the channel controller  403  shown at the top. 
     The channel controller  403  comprises an input/output port part  510 , a control processor  520 , and a memory  530 . 
     The input/output port part  510  receives an access request packet sent from the router  402  through a path  480 . The input/output port parts  510  and  517  may be network interface cards, for example. The control processor  520  performs network protocol processing, including analysis of the access request packet received by the input/output port part  510 , and generates an access request to the memory controller  490 . The control processor  520  enables remote login from external equipment to establish the storage device address. The memory  530  stores a program for controlling data transmission from the input/output port to a data transmission controller  540 , and also stores control information and the received packet. 
     The control processor  520  reads stored packets from the memory  530  and performs network protocol processing. The memory  530  also contains an address management table for managing storage device addresses. 
     The data transmission controller  540  accepts requests from the control processor  520  and performs control of data transmission to a cache. 
     The data transmission controller  540  is connected via an internal path  550  to the coupled unit  430 . 
     The address management table  630  is stored in the memory  530  within the channel controller  403  in the form shown in FIG.  6 . 
     The address given by the storage device IP address  610  is different from the IP address assigned to the channel controller  403 . The channel controller  403  makes the external router  402  believe that there is a device with the storage device IP address. The address given by the storage device MAC address  620  is also different from the MAC address that has been assigned to the channel controller  403 . 
     Next, communication operations in the storage subsystem of the first embodiment of the invention is described with reference to FIG.  4 . 
     FIG. 4 is a conceptual drawing describing the communication operations in the storage subsystem of the first embodiment of the invention. 
     The router  402  and the channel controllers  403  to  410  are interconnected with each other via the input/output ports and an access packet is sent from the host computer  401  to access the storage device  460 . The access packet designates the address of the storage device  460 . 
     Each of the channel controllers  403  to  410 , when it receives a packet sent from the router  402  and the address matches the corresponding storage device address, recognizes it is an access packet to the storage device  460  so as to issue a command to the storage access controller  440  (referring back to FIG. 1) to perform input/output processing. 
     The channel controllers  403  to  410 , jointly or individually, perform a pseudo storage load routing function like a router in balancing the storage load on the storage device  460 , receiving a packet and in responding to the router  402  and reporting that there is a network device with address AD-X on its route. 
     This enables the router  402  to acquire routing information  500 , which can be used for transmitting subsequent packets. To the router  402 , the channel controllers  403  to  410 , jointly or individually, look like a router, which enables optimal packet transmission and balancing the routes for storage. The pseudo storage load routing function enables the channel controllers  403  to  410  to notify the router  402  of current conditions according to a protocol to indicate whether each route connected to the router is available or not. Alternately, the router  402  determines that the corresponding routes are not available due to failure of receiving a response to inquiries within a fixed interval. 
     The pseudo storage load routing function can be controlled by a value given by the state of pseudo function  630  in the address management table. The value ON indicates that the pseudo router function is activated, and the value OFF indicates that the pseudo router function is not activated. The states ON and OFF can be set by the external address establishing means  495 . 
     Although the example shown in FIG. 3 uses a single storage device address, it is possible to have pseudo router functions with a plurality of storage device addresses. 
     Second Embodiment 
     The second embodiment of the invention is described below with reference to FIG.  5  and FIG.  6 . 
     FIG. 5 is a block diagram of the storage subsystem of the second embodiment of the invention. 
     FIG. 6 is a conceptual drawing describing communication operations in the storage subsystem of the second embodiment of the invention. 
     In the first embodiment, the whole storage device  450  in the storage subsystem  470  is assigned with a single storage device address, but in this embodiment, the storage device  450  is assigned with two storage device addresses. 
     Suppose, as shown in FIG. 5, that two different volume groups in the storage device  450  in the storage subsystem are assigned with different storage device addresses AD-X and AD-Y respectively. 
     The channel controllers  403  to  408  in the first group  800 , jointly or individually, have the storage device address AD-X in the address management table  630 , and the channel controllers  409  to  410  in the second group  810 , jointly or individually, have the storage device address AD-Y in the address management table  630 . The pseudo storage load router, i.e. the channel controller  403 - 410  jointly or individually, functions behave as if these addresses existed on the corresponding route therethrough, as described above. 
     The pseudo storage load router generates routing information  501  as shown in FIG. 6 at the router  402 , which uses this information for packet transmission. 
     This enables concurrent access via a network to different volume groups in the storage device  450  from external host computers  401  and  411 . 
     In addition, when more routes are required due to a request from a host computer, it is possible to provide the requested routes by establishing more storage device addresses to be recognized by the channel controllers. 
     The foregoing invention has been described in terms of preferred embodiments. However, those skilled in the art will recognize that many variations of such embodiments exist. Such variations are intended to be within the scope of the present invention and the appended claims.