Abstract:
A PCI-Express slot for coupling devices to a host system is provided. The slot includes a PCI-Express connector that can couple at least two devices using at least two independent PCI-Express lanes. Four, eight, twelve, sixteen, and/or thirty PCI-Express lanes are used to couple at least two devices, and/or eight PCI-Express lanes are used to couple at least two devices.

Description:
BACKGROUND 
   1. Field of the Invention 
   The present invention relates to storage systems, and more particularly, to using PCI-Express standard for connecting plural modules. 
   2. Background of the Invention 
   Storage area networks (“SAN”) are commonly used to store and access data. SAN is a high-speed sub-network of shared storage devices, for example, disks and tape drives. A computer system (may also be referred to as a “host”) can access data stored in the SAN. 
   Typical SAN architecture makes storage devices available to all servers that are connected using a computer network, for example, a local area network or a wide area network. The term server in this context means any computing system or device coupled to a network that manages network resources. For example, a file server is a computer and storage device dedicated to storing files. Any user on the network can store files on the server. A print server is a computer that manages one or more printers, and a network server is a computer that manages network traffic. A database server is a computer system that processes database queries. 
   Various components and standard interfaces are used to move data from host systems to storage devices in a SAN. Fibre channel is one such standard. Fibre channel (incorporated herein by reference in its entirety) is an American National Standard Institute (ANSI) set of standards, which provides a serial transmission protocol for storage and network protocols such as HIPPI, SCSI (small computer system interface), IP, ATM and others. Fibre channel provides an input/output interface to meet the requirements of both channel and network users. 
   Host systems often communicate via a host bus adapter (“HBA”) using the “PCI” bus interface. PCI stands for Peripheral Component Interconnect, a local bus standard that was developed by Intel Corporation®. The PCI standard is incorporated herein by reference in its entirety. Most modern computing systems include a PCI bus in addition to a more general expansion bus (e.g. the ISA bus). PCI is a 64-bit bus and can run at clock speeds of 33 or 66 MHz. 
   PCI-X is a standard bus that is compatible with existing PCI cards using the PCI bus. PCI-X improves the data transfer rate of PCI from 132 MBps to as much as 1 GBps. The PCI-X standard was developed by IBM®, Hewlett Packard Corporation® and Compaq Corporation® to increase performance of high bandwidth devices, such as Gigabit Ethernet standard and Fibre Channel Standard, and processors that are part of a cluster. 
   PCI-Express (may also be referred to as “PCI-Exp”) is another industry standard that is being developed to allow data transfer at 2.5 Gigabits/second and has a layered structure. PCI-Exp provides a dual-simplex channel that is implemented as a transmit and receive pair. 
   PCI-Exp link consists of two low-voltage, differentially driven pair of signals, i.e. a transmit pair and a receive pair. A data clock is embedded using an 8b/10b-encoding scheme to achieve high data rates. A PCI-Exp physical layer is used to transport packets between link layers of two PCI-Exp agents. Adding signal pairs to form multiple lanes may linearly scale the bandwidth of a PCI-Exp lane. The current PCI-Exp physical layer can support a ×1(single), ×2 (double), ×4 (four), ×8(eight), ×12 (twelve), ×16(sixteen) and ×32 (thirty two) lane widths. 
   As discussed above, servers to interact with storage sub-systems use adapters. Often multiple adapters are used in complex systems. In order to couple plural adapters to a host system (for example, the host system  101 A,  FIG. 1A ), a bridge is required.  FIG. 1D  block diagram shows two adapters (A and B)  106  that are coupled to a bridge  106 A allowing host system  101 A access to both the adapters A and B. The cost of using bridge  106 A is not commercially desirable. 
   Therefore, there is a need for a system that allows multiple adapters to be coupled to a host system without using a bridge and preferably using the same PCI-Exp slot. 
   SUMMARY OF THE INVENTION 
   In one aspect of the present invention, a PCI-Express slot for coupling devices to a host system is provided. The slot includes a PCI-Express connector that can couple at least two devices using at least two independent PCI-Express lanes. Four, eight, twelve, sixteen, and/or thirty PCI-Express lanes are used to couple at least two devices, and/or eight PCI-Express lanes are used to couple at least two devices. 
   In another aspect of the present invention, a system for coupling plural adapters to a host system is provided. A motherboard with a PCI-Express slot having a PCI-Express connector that can couple at least two devices using at least two independent PCI-Express lanes. 
   In yet another aspect of the present invention, a PCI-Express connector in a PCI-Express slot for coupling devices to a host system is provided, where the connector can couple at least two devices using at least two independent PCI-Express lanes. 
   In one aspect of the present invention, a bridge is not needed to couple plural adapters to a host system using the PCI-Exp bus. 
   This brief summary has been provided so that the nature of the invention may be understood quickly. A more complete understanding of the invention can be obtained by reference to the following detailed description of the preferred embodiments thereof concerning the attached drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing features and other features of the present invention will now be described with reference to the drawings of a preferred embodiment. In the drawings, the same components have the same reference numerals. The illustrated embodiment is intended to illustrate, but not to limit the invention. The drawings include the following Figures: 
       FIG. 1A  shows a host system with an adapter coupled to a storage subsystem, used according to one aspect of the present invention; 
       FIG. 1B  shows a block diagram with details of an adapter, used according to one aspect of the present invention; 
       FIG. 1C  shows the internal architecture of a host system, used according to one aspect of the present invention; 
       FIG. 1D  shows a top-level block diagram where two adapters are connected to a host system using a bridge; 
       FIGS. 2A and 2B  show block diagrams where the same PCI-Exp connector is used to couple more than one adapter, according to one aspect of the present invention; and 
       FIGS. 2C and 2D  show a block diagram where the same PCI-Exp connector is used to couple plural adapters, according to one aspect of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   To facilitate an understanding of the preferred embodiment, the general architecture and operation of a system using storage devices will be described. The specific architecture and operation of the preferred embodiment will then be described with reference to the general architecture. 
     FIG. 1A  shows a host system  101 A with memory  101  coupled to a SAN  115  that is coupled to storage subsystem  115 . In the  FIG. 1B  example, Host  101 A has access to storage sub-systems  116  and  118 . It is noteworthy that a host system  101 A, as referred to herein, may include a computer, server or other similar devices, which may be coupled to storage systems. Host system  101 A includes a host processor, random access memory (“RAM”), and read only memory (“ROM”), and other components to communicate with various SAN modules, as described below. 
     FIG. 1B  shows a system  100  that uses a controller/adapter  106  (referred to as “adapter”  106 ) for communication between a host system  101 A with host memory  101  to various storage systems (for example, storage subsystem  116  and  121 , tape library  118  and  120 ) using fibre channel storage area networks  114  and  115 . Servers  117  and  119  can also access the storage sub-systems (for example,  116  and  121 ) using SAN  115  and  114 , respectively. 
   Host system  101 A communicates with adapter  106  via a PCI-Exp bus  105  through a PCI-Exp interface  107 . Adapter  106  includes processors  112  and  109  for the receive and transmit side, respectively. Processor  109  and  112  may be a RISC processor. 
   Transmit path in this context means data coming from host memory  101  to the storage systems via adapter  106 . Receive path means data coming from storage subsystem via adapter  106 . It is noteworthy, that only one processor can be used for receive and transmit paths, and the present invention is not limited to any particular number/type of processors. 
   Adapter  106  also includes fibre channel interface (also referred to as fibre channel protocol manager “FPM”)  122  and  113  in receive and transmit paths, respectively. FPM  122  and  113  allow data to move to/from storage systems  116 ,  118 ,  120  and  121 . 
   Adapter  106  includes external memory  108  and  110  and frame buffers  111 A and  111 B that are used to move information to and from the host to other SAN components. 
   Host memory  101  includes a response queue  104  and a request queue  103  to move information to and from host memory  101  using a driver  102 . 
     FIG. 1C  is a block diagram showing the internal functional architecture of host system  101 A. As shown in  FIG. 1C , host system  101 A includes a microprocessor or central processing unit (“CPU”)  124  for executing computer-executable process steps and interfaces with a computer bus  125  (similar to PCI-Exp bus  105 ). Also shown in  FIG. 1C  is an adapter interface  126  (similar to PCI-Exp interface  107 ) that interfaces host system  101 A with adapter  106 . Host system  101 A also includes a display device interface  127 , a keyboard interface  128 , a pointing device interface  132 , and a storage device  129  (for example, a disk, CD-ROM or any other device). 
   Storage  129  stores operating system program files, application program files, and other files. Some of these files are stored on storage  129  using an installation program. For example, CPU  124  executes computer-executable process steps of an installation program so that CPU  124  can properly execute the application program. 
   A random access main memory (“RAM”)  130  also interfaces to computer bus  125  to provide CPU  124  with access to memory storage. When executing stored computer-executable process steps from storage  129 , CPU  124  stores and executes the process steps out of RAM  130 . 
   Read only memory (“ROM”)  131  is provided to store invariant instruction sequences such as start-up instruction sequences or basic input/output operating system (BIOS) sequences for operation of a keyboard (not shown). 
     FIG. 2A  shows a block diagram where a motherboard  200  is used in host system  101 A and includes a PCI-Exp slot  201 . Slot  201  includes a PCI-Exp connector  201 A ( FIG. 2B ). A card  203  is placed in slot  201  and connector  201 A is used to connect two adapters (A and B)  106  to host system  101 A. 
   It is noteworthy that although the example in  FIGS. 2A and 2B  show two adapters, the present adaptive aspects of the present invention are not limited to any particular number of adapters. For example, in  FIG. 2C , PCI-Exp slot  201  is shown where two devices  201 G and  201 B (adapters A and B) are coupled using ×4 (i.e. 4 lanes each) in an ×4 configuration.  FIG. 2D  also shows PCI-Exp slot  201  that couples four devices  201 C- 201 F using the ×2 (two lanes) configuration. Similarly, other devices can be used in ×12, ×16 and ×32 configuration. 
   Although the foregoing examples show how adapters in the SAN environment being coupled using the PCI-Exp bus, the present invention is not limited to any particular type of adapter. For example, plural cards in other environments (for example, multi-media, graphics, or printing) may be coupled using the adaptive aspects of the present invention. 
   In one aspect of the present invention, a bridge is not needed to couple plural adapters to a host system using the PCI-Exp bus. 
   Although the present invention has been described with reference to specific embodiments, these embodiments are illustrative only and not limiting. Many other applications and embodiments of the present invention will be apparent in light of this disclosure and the following claims.