Cabling picker in a library of stationary memory devices

[0002] The present invention relates to a method and apparatus for interconnecting a computer with selected memory devices in a library of memory devices.

[0003] Large scale computing devices often employ a library of removable computer memory media to provide for increased storage capability and the sharing of media by multiple hosts. In such a library, the media are shelved in storage bins for retrieval by a robotic picking apparatus or “picker.” Such a picker for optical disk media is described in Dimitri et al., U.S. Pat. No. 5,377,121, which is herein incorporated by reference in its entirety. Tape cassettes are another common library media. The library has at least one drive receptacle coupled to one or more host computers that may read or write to the media.

[0004] When a host requests a particular medium in the library, the picker is typically commanded to travel to the storage bin in the library where the medium is shelved, grip the medium, remove the medium from the storage bin, travel to a destination drive having input/output (“I/O”) connections with the host, insert the medium into the drive, and power the drive.

[0005] A problem with these prior art libraries is that optical media provides relatively slow reading and writing, while tape media provides relatively slow random access.

[0006] In recognition of these problems, the concept of a library of hard disk drives was developed, which is the subject of the assignee's companion application entitled LIBRARY OF HARD DISK DRIVES WITH TRANSPARENT EMULATING INTERFACE, executed on Apr. 19, 2001 by inventors Kamal Dimitri, Robert G. Emberty, Craig Klein, and Daniel J. Winarski, filed on Apr. 26, 2001, and incorporated herein by reference in its entirety. According to the concept, hard disk drives are stored in associated storage locations in the library. The robotic picker is adapted to couple and decouple a selected disk drive from a destination receptacle that is coupled to the one or more host computers requesting data.

[0007] The hard disk drive library provides the advantage of relative speed as compared to libraries employing optical or tape media. Entire hard disk drives, rather than hard disk media, are exchanged in the library to remain within the close mechanical tolerances required for efficient use of this memory element.

[0008] In a basic form of the concept, the destination receptacle provides power connections to the disk drive and I/O connections to the host computers, and the robotic picker retrieves the selected disk drive from its storage location, carries the disk drive to and inserts the disk drive into the destination receptacle. The disk drive is then powered and spins up to its operating speed. Finally, when this operating speed is reached, the data on the disk drive may be accessed by the computer.

[0009] As may be readily appreciated, the movements required for accessing either media or drives in the library takes time, and efforts are constantly being made to decrease the time required.

[0010] Accordingly, there is a need for a cabling picker in a library of stationary memory devices that provides for decreasing the time and cost required to match a host computer with a selected memory device in the library.

[0011] Disclosed is a cabling picker in a library of stationary memory devices. One or more input/output cables electrically connected to a host computer through a destination are provided, and these are moved or manipulated for interconnecting with selected memory devices in the library instead of moving the memory devices to the destination.

[0012] Therefore, it is a principal object of the present invention to provide a novel cabling picker in a library of stationary memory devices.

[0013] It is another object of the present invention to provide a cabling picker in a library of stationary memory devices that provides for increasing the speed with which a selected memory device in the library may be connected to a host computer.

[0014] It is yet another object of the present invention to provide a cabling picker in a library of stationary memory devices that provides for decreasing the cost of the apparatus employed for connecting a selected memory device in the library to a host computer.

[0015] The foregoing and other objects, features and advantages of the present invention will be more readily understood upon consideration of the following detailed description of the invention, taken in conjunction with the following drawings.

[0016] FIG. 1 is a pictorial schematic illustrating a cabling picker in a library of stationary memory devices according to the present invention.

[0017] FIG. 2 is a pictorial schematic illustrating a first embodiment of a method for using a cabling picker according to the present invention.

[0018] FIG. 3 is a pictorial schematic illustrating another embodiment of a method for using a cabling picker according to the present invention.

[0019] FIG. 4 is a pictorial schematic illustrating a prior art distance of travel for a prior art picker in a library of memory devices.

[0020] FIG. 5 is a pictorial schematic illustrating a distance of travel for a cabling picker according to the present invention.

[0021] FIG. 6 is a pictorial schematic illustrating yet another embodiment of a method for using a cabling picker according to the present invention.

[0022] Referring to FIG. 1, a library 10 is shown for use with the present invention. The library 10 includes a number of individual storage bins 12 for shelving individual memory devices or media therefor, such as hard disk drives, optical disk drives, and flash memory modules (hereinafter “devices”). Preferably, the memory devices are hard disk drives; however, the library may be adapted to for use with other computer memory devices, such as optical and tape media, and flash memory modules without departing from the principles of the invention. The bins 12 may also be used or particularly adapted for shelving cabling as described below.

[0023] The memory devices are typically accessed by a robotic picking apparatus 16 known as a “picker;” however the “picker” may be a human operator without departing from the principles of the invention. The library typically includes a controller which commands movements of the picker as described below, as well as carries out communications with one or more host computer(s) requesting access to the memory devices, such as described in the aforementioned companion application. The controller may be a general or special purpose computer.

[0024] The storage bins 12 are typically organized in a two-dimensional matrix, such as indicated by the coordinate system X-Z in FIG. 1. However, the storage bins may be organized into multiple two dimensional matrices, one or more linear arrays or one or more three-dimensional matrices as well, wherein a matrix may be any geometric shape such as but not limited to a square or circle, or a cube, cylinder or sphere. The picker is adapted to travel the extent of the dimensions required to visit any selected storage bin. The matrix shown is square to minimize the maximum distances the picker must travel.

[0025] In the prior art, the picker visits a selected storage bin in order to retrieve the memory device shelved there, brings it to a destination or library backplane which is electrically connected to a host computer, and installs the memory device into the backplane. When the host computer is finished with one memory device and requests access to another, the picker removes the first memory device from the destination backplane, travels to the storage bin shelving the second memory device, withdraws the second memory device from the storage bin and replaces it with the first memory device, and returns to the destination backplane to install the second memory device.

[0026] By contrast, according to the invention, some of the storage bins 12 are employed for storing I/O and power cables 18 (hereinafter “cables”) necessary to mechanically and electrically connect a selected one of the memory devices 14 with the destination backplane to permit data communications therebetween. The cables 18 have connecting ends that include standard connectors for this purpose. Preferably, the cables include metal wires for transmitting data to gain the advantage of mechanical durability and robustness, though the wires are preferably used to transmit data using according to a fibre channel architecture.

[0027] In the typical library environment, there will be a substantially greater number of storage bins devoted to shelving memory devices than are needed to shelve cables. A relatively small subset of the storage bins 12 are therefore selected for cable storage and, according to a first aspect of the invention, are preferably disposed at or near the center of the matrix. For example, in FIG. 1 a middle row in the matrix is selected for storing cables 18 in preference to a top or bottom row.

[0028] The picker is adapted to grip a connecting end 20 of the cables 18, mechanically connect the connecting end to selected memory devices, and mechanically disconnect the connecting end from the memory device. Mechanisms for satisfying this purpose will be apparent to persons of ordinary skill in the art and need not be described.

[0029] Referring to FIG. 2, in a first embodiment of the invention, each cable is adapted to reach from the storage bin in which it resides to the storage bin that is the farthest distance away. When a host computer to which a cable 18ais connected requests data resident in a memory device that is shelved in a particular storage bin 12am, the picker 16 travels to the storage bin 12acshelving the cable 18a, grabs the end 20aof the cable, travels to the storage bin 12amwith the end of the cable, and connects the end of the cable to the memory device. The cables are preferably retractably stored on the storage bins, such as by use of spring loaded reels, or concentrically coiled springs, so that they will return to their respective storage bins when disconnected at the memory device by the picker.

[0030] In a second embodiment of the invention, the picker 16 anticipates that the cable 18awill be connected to a memory device in the future and carries the end 20aof the cable 18awith it during its rounds so that it is “ready” to move to a requested memory device without first visiting the storage bin 12acshelving the cable. The decision to keep the cable 18aready may be based, e.g., on the frequency of past requests for data by a particular computer.

[0031] Turning to FIG. 3, in a third embodiment of the invention, a switching matrix 30 may be provided wherein the cables 18 are arranged in rows (or columns) and additional memory device cables 22 connected to the memory devices are arranged in columns (or rows). The columns define a first plane and the rows define a second plane that is spaced from the first plane, for normally preventing electrical contact at the points or potential “nodes” 24 corresponding to a it crossing of the cables 18 and the cables 22. However, at each node the cables 18 and 22 may be provided with an electrical switch which may be toggled by the picker to complete an electrical interconnection between a selected cable and memory device. As an alternative, each node may include a connector pair that can be mechanically connected and disconnected by the picker. As another alternative, a jumper cable may be used to jumper between a selected cable 18 and a selected cable 22, either at the node 24 or at some other locations of these cables. Where jumper cables are used, there may be no need to organize the cables 18 and 22 so that they cross as aforedescribed, depending on the length of the jumper cables. In that regard, it may be noted for conceptual purposes that if the length of the jumper cables is lengthened to become comparable to the length of the cables 22, the cables 22 may be replaced with the jumper cables wherein the alternative essentially degenerates to become the first embodiment described above.

[0032] The present invention provides a substantial increase in speed for at least two reasons. One of these is that the picker may be moved about the library more quickly. The cables 18 are less massive than the memory devices themselves, and the picker itself may be constructed to be less massive because of the reduction in the mass of its load. Another reason that the invention provides an increase in speed is that the distance the picker must travel is at least potentially reduced.

[0033] FIG. 4 shows the distance a prior art picker 24 must travel to process a typical request for data resident in a particular disk drive. The picker 24, starting at an arbitrary location A, was required to move to the location B for the memory device, and then move to the location C of the destination, wherein movements in the Y axis are ignored for simplicity. The total distance traveled is the distance from A to B, plus the distance from B to C. Both of these distances are, on average, the same, and are related to the dimensional extent of the matrix, assuming that the requests for data are distributed randomly over the storage bins 12.

[0034] Turning to FIG. 5, by contrast, the picker 16 according to the present invention may move from the arbitrary location A to a location D for a cable connected to the destination C, and then on to the location B for the memory device. The total distance traveled is the distance from A to D, plus the distance from D to B. This total distance may be on average less than the total distance A to B plus the distance B to C shown in FIG. 4 because the cables may be grouped in a dimensionally small subset of the space devoted to the memory devices and may be strategically positioned near or at the middle of the matrix.

[0035] According to the second embodiment of the invention, the picker moves from the arbitrary location A directly to the location B of the memory device, providing a further decrease in distance traveled by the picker. According to the third embodiment of the invention, the picker moves from the arbitrary location A directly to the node corresponding to the desired interconnection. Since the area devoted to the nodes may be substantially less than the area devoted to the memory devices themselves, this provides a still further decrease in the distance that the picker is required to travel.

[0036] Turning to FIG. 6, yet another embodiment of the invention is illustrated. It is recognized that there is typically a much larger number of memory devices in the library than host computers accessing the memory devices. According to the invention, the cables 18 may therefore be provided advantageously around the perimeter of a matrix 40 of the storage bins 12. Moreover, multiple copies of the cables 18 provided around corresponding multiple sides of the matrix may be bussed together and connected to respective hosts. For example, shown in FIG. 6 is a bus 42 that connects, e.g., four cables 18a, 18b, 18c, and 18dto a host computer #1. Similarly, a bus is provided to connect, e.g., four cables respectively to host computer #'s 2-5.

[0037] To illustrate the principle of this aspect of the invention further, suppose it is desired to connect the following host computers to the memory devices in the following storage bins: computer #1 with storage bin E; computer #2 with storage bin F, computer #3 with storage bin G, computer #4 with storage bin H, and computer #5 with storage bin J. It may be appreciated that, in general, there is a likelihood that at least some of the cables will cross one another. Such crossings have the potential for reducing speed. For example, to disconnect a first cable from one memory device and return the cable or the end of the cable to its storage bin, it may be necessary to wait until a second cable which crosses the first cable is put away or moved to avoid creating a knot.

[0038] More particularly, in FIG. 6 five cables 18a1, 18a2, 18a3, 18a4 and 18a5 are provided on the left hand side of the matrix 40. Each cable is connected to a respective host computer 1-5. If cable 18a5 is connected to the memory device at the storage bin J, it will cross the cable 18a4 which is connected to the memory device at the storage bin H. However, connecting cable 18c5 on the right hand side of the matrix 40 to the memory device at storage bin J eliminates the cross-over.

[0039] As many instances “n” of cables 18nh(for “h” host computers) may be provided as desired, wherein a larger value of n provides a greater likelihood that random connections between the host computers and the memory devices distributed throughout the library can be made without cross-overs.

[0040] The picker may respond to a computation of the shortest connection path available between cables 18nhfor a given host computer h₁, e.g., 18n₁h₁. Alternatively, the picker may respond to a modified decision not to select this shortest path as a result of determining that a cross-over with another cable will be produced thereby. The picker may then employ another path using another cable 18n₂h₁that, though it increases the distance the picker must travel, also increases the likelihood that maximum speed for the system as a whole is achieved by avoiding potential entanglements with other cables. Moreover, the decision regarding which path to take may be informed by the frequency of past requests for particular data by particular computers.

[0041] While applicable to memory devices generally, the present invention provides particular advantage for accessing mechanical media such as hard disk drives, because these are relatively heavy and therefore must be moved relatively slowly. Moreover, in accord with the invention, power may be provided at each of the storage bins 12 rather than with the I/O cabling moved by the picker, and the disk drives may be spun up during the time the picker is traveling thereto, still further reducing access time.

[0042] It is to be recognized that, while a particular cabling picker in a library of stationary disk drives has been shown and described as preferred, other configurations and methods could be utilized, in addition to those already mentioned, without departing from the principles of the invention.

[0043] The terms and expressions which have been employed in the foregoing specification are used therein as terms of description and not of limitation, and there is no intention of the use of such terms and expressions of excluding equivalents of the features shown and described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims which follow.