Abstract:
Provided are a method, system, and program for adding a fourth device to a network including a first, second, and third devices, wherein the first and second devices are directly connected to the third device. The fourth device is directly connected to the third device while the first and second devices remain connected to the third device, and wherein the first and second devices continue to have access to the third device while the fourth device is connected to the third device.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a system for enabling connection among devices in a network. 
     2. Description of the Related Art 
     In a Fibre Channel Arbitrated Loop networks, devices are connected to one another to form a “loop” architecture, where all devices may communicate with any device in the loop. The connections are made with optical fibers or copper lines, which provide high bandwidth communication between the devices. Devices may be connected to the loop through two ports, where one port is used as a receiver and another as a transmitter. In such implementations, each fiber cable is attached to a transmitter of a port at one end and a receiver of another port at the other end. Alternatively, a single cable may be used for both receiving and transmitting data. In such case, the device need only have a single connection to another device in the loop. Devices connected in a Fibre Channel arbitrated loop may form a Storage Area Network (SAN), which may include numerous interconnected Fibre Channel Arbitrated Loops. 
     In one known architecture, a storage device drawer may include multiple hard disk drives and have two adaptor cards. Each adaptor card on the drawer may connect to an adaptor on a separate host system, where the fibre cable between each host and the drawer is bi-directional. Further, drawers may be daisy chained together, such that one host is connected to one storage drawer adaptor, and the other storage drawer adaptor is connected to an additional drawer. Any number of additional drawers may be daisy chained together, with the second host attached to the second adaptor of the last drawer in the daisy chain. 
     To add a drawer to the loop, if a drawer is connected to two separate hosts, then an administrator has to disconnect one host from one drawer adaptor, connect a cable between the new drawer and the drawer adaptor from which the host was disconnected, and then reconnect the host to the second adaptor on the new drawer. When the host is disconnected from the drawer, the Fibre Channel performs a loop initialization routine to configure the new arrangement. While the host remains disconnected, users can access data to the host remaining connected, but any users that accessed the loop through the disconnected host remain off-line and unable to access the data stored in the storage drawers. This downtime can be problematic, especially if the administrator takes a significant amount of time to connect the disconnected host to the new drawer. 
     Accordingly, there is a need in the art for improved techniques for adding devices to a loop. 
     SUMMARY OF THE DESCRIBED IMPLEMENTATIONS 
     Provided are a method, system, and program for adding a fourth device to a network including a first, second, and third devices, wherein the first and second devices are directly connected to the third device. The fourth device is directly connected to the third device while the first and second devices remain connected to the third device, and wherein the first and second devices continue to have access to the third device while the fourth device is connected to the third device. 
     In further implementations, the first and second devices access to the third device is only interrupted during an initialization procedure executed when the fourth device is connected to the third adaptor to recognize the fourth device. 
     In still further implementations, the first and second devices comprise host systems and wherein the third and fourth devices comprise storage devices. 
     Yet further, the third device may include three adaptor cards, wherein the first and second devices are each connected to one separate adaptor card in the third device, and wherein connecting the fourth device to the third device comprises connecting an adaptor card on the third device to one of the available adaptor cards in the third device. 
     Described implementations provide apparatus and techniques for connecting one additional device to another device in a manner that allows other devices to remain connected to the device to which the additional device is being connected. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Referring now to the drawings in which like reference numbers represent corresponding parts throughout: 
         FIGS. 1 ,  2 , and  3  illustrate network devices connected in accordance with implementations of the invention; and 
         FIG. 4  illustrates an architecture of computing components in the network environment, such as the hosts and storage devices, and any other computing devices. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following description, reference is made to the accompanying drawings which form a part hereof and which illustrate several embodiments of the present invention. It is understood that other embodiments may be utilized and structural and operational changes may be made without departing from the scope of the present invention. 
       FIG. 1  illustrates a loop network architecture  2  in accordance with implementations of the invention. Two hosts  4   a ,  4   b  each having host bus adaptors (HBAs)  6   a ,  6   b  connect to a separate device adaptor (DA)  8   a  and  8   b  on storage device  10 , which has an additional device adaptor  8   c  comprising a bypass circuit. Each of the adaptors  8   a ,  8   b , and  8   c  may comprise device adaptors known in the art for connecting a device to a network, such as a Fibre Channel Arbitrated Loop. The cables  12  and  14  connecting the hosts  4   a  and  4   b  to adaptors  8   a  and  8   b  may enable bidirectional communication therebetween. The hosts  4   a ,  4   b  may comprise any type of computer system known in the art, including a server capable of managing data access requests from attached clients to any storage devices in the loop  2 . The storage device  10  may comprise a “drawer”, having numerous interconnected hard disk drives. The hard disk drives  10  in the storage device  10  may be configured as a Redundant Array of Independent Disks (RAID), Just a Bunch of Disks (JBOD), a Direct Access Storage Device (DASD), etc. 
       FIG. 2  illustrates the state of the network after a storage device  20  having at least two adaptors  28   a ,  28   b ,  28   c , three are shown, is added to the network  2 . To add the storage device  20 , the administrator would connect a cable from the third bypass adaptor  8   c  in storage device  10  to one of the adaptors  28   a ,  28   b , or  28   c . Upon connecting storage device  20  to the bypass adaptor  8   c , a loop initialization routine, such as the Fibre Channel Arbitrated Loop initialization routine, would be performed to recognize the added storage device  20  and make the storage device  20  available to all other devices in the loop network  2 , including hosts  4   a ,  4   b . Because the loop initialization time is very fast, the hosts  4   a ,  4   b  appear to have continued access to the storage device  10  while storage device  20  is added to the loop  2 . The host  4   a ,  4   b  access is only briefly disrupted during the initialization operation. There are no interruptions due to physically disconnecting one host  4   a ,  4   b  from the storage device  10  to add another storage device  20 , because the new storage device  20  is connected to the bypass adaptor  8   c.    
     Moreover, interruptions would further be minimized when removing the storage device  20  that was added to the third bypass adaptor  8   c  of the storage device  10  connected to the two hosts  4   a ,  4   b . With the described implementations, the storage device  20  is removed by disconnecting the storage device  20  from the bypass adaptor  8   c  which does not require any physical disruption to the connection with the hosts  4   a ,  4   b  through device adaptors  8   a ,  8   b.    
     With the described implementation, when adding the new storage device, the cables connecting to the hosts remain undisturbed and continue to be used, thereby avoiding any disruption in host access to the storage device  10 . In the prior art, when disconnecting a host from a storage device to add a new storage device, and then reconnecting the disconnected host to the added storage device, a cable of different length may be needed because the host is being connected to a new storage device, which may be located at a different distance from the host than the storage device to which the host was previously connected. In the prior art, the duration of the disconnection may be extended if the administrator has to locate a cable of appropriate length to connect the host to the new storage device. With the described implementations, there are no such delays because the hosts remain connected to the storage device while the new storage device is added to the loop. 
       FIG. 4  illustrates one implementation of a computer architecture  200  of the network components, such as the hosts and storage devices shown in  FIGS. 1 ,  2 , and  3 . The architecture  200  may include a processor  202  (e.g., a microprocessor), a memory  204  (e.g., a volatile memory device), and storage  206  (e.g., a non-volatile storage, such as magnetic disk drives, optical disk drives, a tape drive, etc.). The storage  206  may comprise an internal storage device or an attached or network accessible storage. Programs in the storage  206  are loaded into the memory  204  and executed by the processor  202  in a manner known in the art. The architecture further includes a network card  208  to enable communication with a network, such as a Fibre Channel Arbitrated Loop. As discussed, certain of the network devices may have multiple network cards. An input device  210  is used to provide user input to the processor  202 , and may include a keyboard, mouse, pen-stylus, microphone, touch sensitive display screen, or any other activation or input mechanism known in the art. An output device  212  is capable of rendering information transmitted from the processor  202 , or other component, such as a display monitor, printer, storage, etc. 
     In the described implementations, the hosts included one host bus adaptor and the storage devices had three adaptors. In alternative implementations, the hosts may have multiple host bus adaptors or multiple ports on one HBA. Further, devices other than storage devices may be designed to have three adaptors capable of providing separate bidirectional connection with other network devices. Still further, if the cables only allow for unidirectional communication, then each adaptor would need two ports to connect to each device, one for transmitting and one for receiving. 
     In further implementations, the hosts may connect to different ports on the same adaptor in the storage device, thereby requiring fewer adaptors to enable the storage drawer to separately connect to three other devices. 
     The foregoing description of various implementations of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto. The above specification, examples and data provide a complete description of the manufacture and use of the composition of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended.