Abstract:
Modular disk storage modules are combined to form an expandable disk drive base data storage system. Additional modules containing disk drives can be added to the system as memory requirements increases. Data and parity information is distributed amongst three or more disk drives in order to enable data recovery if one of the disk drives ceases to function properly.

Description:
This application is a continuation of application Ser. No. 07/932,794, filed Aug. 20, 1992, now abandoned. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to disk drive based data storage systems. More particularly, the present invention relates to modular disk drive expansion capabilities for computers. 
     BACKGROUND OF THE INVENTION 
     Most computers employ Winchester (hard) type disk drives to store programs and data. The data capacity of the particular disk drive depends on the user&#39;s anticipated storage requirements. It is often difficult to add data storage capability to a computer system once it has been configured. This difficulty is usually more dominant with personal computer type systems, but can present itself with work stations, as well as larger systems. 
     External disk drive storage systems, which were often referred to as “Bernouli Boxes”, have provided the capability for adding an external disk drive to replace or augment the internal disk drive of a personal computer or work station. Several different data protocols have been adapted for use in conjunction with external data storage systems. These protocols are used in some systems to transfer data between internal components as well. The most popular of these protocols are the Small Computer Systems Interface (SCSI) and Enhanced Small Device Interface (ESDI). The SCSI and ESDI protocols and associated hardware allow data flow at rates of several megahertz, whereas Disk Operating System (DOS) data transfer rates have difficulty achieving these data transfer rates. Transfer rates of 5 megahertz or more are fairly common using the SCSI interface. 
     In most systems, a single power supply is coupled to a number of individual peripheral components including disk drives. The capacity of the system power supply is predetermined, and is based on the expected load that the system is anticipated to draw. Increasing the number of peripheral devices, or the capacity of peripheral devices such as disk drives results in a requirement for additional power which may have been unanticipated. As a result, it may be necessary to replace the power supply once it has been determined that it is necessary to expand the system capabilities. 
     When the power supply capabilities are expanded, an attempt is made to determine whether the new power supply will accommodate the future power supply requirements of the system. Future expansion beyond the anticipated load necessitates replacing the power supply again. 
     When hard disk drives were originally introduced, failure of the hard disk drive to maintain data, or to be able to recover the data was not uncommon. As a result, most users instituted rigid back-up programs using removable media such as floppy disk drive and tape back ups. As hard disk drives have become more reliable, many users have reduced their reliance on backing up the data stored within the system. 
     Hard disk drives have also increased in capacity from relatively modest levels of 10 megabytes to higher density, higher capacity levels approaching 2000 megabytes, and beyond. Backing up a hard disk which held 10 megabytes may have been reasonably time consuming, but backing up a hard disk which may have 100 or 200 times as much data becomes significantly more time consuming. As a result, users have become less diligent in their efforts to back up data from a hard disk drive. 
     This has resulted in an increased exposure to the user of a computer system should a single hard disk drive crash, or otherwise cease to function properly. The amount of data which may be irretrievably lost can be enormous. The consequences to the system user can be catastrophic. Data recovering centers exist, but may or may not be able to successfully recover the data from a particular hard disk drive, or may take several months to do so. Given the timelines of information in most applications, this becomes unacceptable. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide an easily expandable hard disk drive storage system which can be easily added to without requiring replacement of a power supply, or other integral components. 
     It is a further object of the present invention to provide a modular expansion system so that the entire system&#39;s capability in the future is not restricted by choices made when the system is initially purchased. 
     It is a further object of the present invention to provide the capability for versatile selection of data transfer systems and organization. 
     It is a further object of the present invention to provide a high speed data transfer capability between the computer and external peripherals such as disk drives. 
     It is a further object of the present invention to provide a data storage system from which the data can be easily recovered, or reconstructed should a single hard disk drive fail. 
     It is a further object of the present invention to provide a versatile disk drive storage system which can be easily expanded after it is in use without sacrificing the data recovery capability of the system. 
     One feature of the present invention involves the use of a modular design in which peripheral devices such as hard disk drives are added in uniform stackable modules which include self contained power supplies. The individual modules interconnect mechanically to form a single structure which can be easily added to, or subtracted from. 
     Another feature of the invention involves the use of a number of individual, short interconnection cables to connect each of the modules together in order to route electrical power between the modules, as well as routing data transfer signals. 
     Another Embodiment of the present invention distributes data to be stored amongst three or more individual hard disk drives in order to allow data recovery from the remaining hard disk drives if a single hard disk drive ceases to function. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows the interconnection of the storage modules illustrating an embodiment of the present invention with a host computer. 
     FIG. 2 is a detailed assembly drawing of the illustrated embodiment of FIG.  1 . 
     FIG. 3 is a front view of two modules of the illustrated embodiment of FIG. 1 fully assembled. 
     FIG. 4 is a schematic diagram of the circuitry of the modules of the illustrated embodiment of FIG.  1 . 
     FIG. 5 is an illustration of the physical layout of the modules of the illustrated embodiment of FIG.  1 . 
     FIG. 6 is an illustration of an alternative embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, a personal computer  20  having a monitor  22  and a keyboard (not shown) is connected to the expandable disk drive assembly  28  of the present invention by inserting a communication card  24  such as a SCSI adaptor card into computer  20  and connecting it through cable  26  to system  28 . 
     The expandable disk drive storage system  28  consists of one or more disk drive modules  30 . Disk drive modules  30  may be stacked upon one another as shown in FIG.  1 . They are fastened together to prevent the upper units from slipping with respect to the lower units by screws or other suitable fasteners. The bottom module  30  in the stack has a power cord  32  which connects the power supply in the bottom module  30  to a power source, such as 110 volts alternating current available from most appliance outlets. Bottom module  30  is also connected to personal computer  20  through cable  26 . These connections are made in the front of module  30 . Panel cover  34  snaps into the front, lower portion of bottom module  30  to cover the power connector and cable  32  as well as the computer connector and cable  26 . Non-skid feet  64  attached under bottom module  30  to prevent bottom module  30  from sliding on a table or other work surface. 
     Successive modules  30  are placed on top of the bottom module  30  and fastened by suitable fasteners to prevent the modules from moving with respect to each other. Interconnection between adjacent modules  30  is accomplished by power connector assembly  36  and computer connector assembly  38 . These connectors are extremely short in length, and the interconnections are accomplished from the front of the modules  30 . This avoids the need to route individual power cables  32 , or computer interconnection cables  26  for each of the modules added to the system. Additionally, by providing all of the interconnection wiring on the front of module  30 , it is not necessary to swivel the modules around to access the rear panel, or rear portion of modules  30  in order to interconnect them with the computer  22 , or each other. This also eliminates the need to route interconnection cables from the front of one module  30  to the rear of a subsequent module  30 . 
     Modules  30  consist of an outer housing  44  and an internal, removable assembly  46 . Assembly  46  is slid into case  44  along tracks  50 . Latches  48  located on both sides of removable assembly  46  prevent removable assembly  46  from sliding out of housing  44 . A top panel  52  may be placed on top of the top module  30  of the stack. This provides for closure of the system, sealing assembly holes which are located on the top of the module  30 . These assembly holes include holes  60  and  62  which are located in the top of each of the modules  30 . Assembly holes  60  and  62  are threaded, and allow a case  44  to be fastened to a lower module  30  by placing screws through matching holes in the bottom of case  44  through threaded openings  60  and  62  of module  30  located beneath case  44 . The removable assembly  46  is then slid into case  44 . 
     Depending on the particular data transfer protocol selected, it may be necessary to provide a resistive terminator such as terminator  40  on the connector of the last module in the chain of the system. This reduces, or eliminates signal reflection at high frequencies due to an unterminated transmission line. A connector panel  42  is snapped into the front section of adjacent modules  30  to cover connectors  36  and  38 , and provide a more aesthetically pleasing appearance of the system. Top panel  52  has a front portion  54  which covers the terminator  40  and connector area of the top module  30 . 
     Referring to FIG. 2, the lower portion of the disk drive expansion stack  28  is shown in a partially assembled condition. A bottom module  30  with a front panel  34  is shown located beneath a middle module  30 . Connector panel  42  is shown located beneath lower module  30  and middle module  30 . Upper module  30  is shown broken apart so that it can be seen in more detail. Outer case  44  as shown in FIG. 1 is a two part assembly consisting of a base  70  and a top cover  72 . Removable assembly  46  is shown located between base  70  and outer cover  72 . Tracks  50  are located on the left and right sides of base member  70 . For the purposes of explanation, removable assembly  46  is also shown in an expanded view. 
     Removable assembly  46  consists of a base tray  80  and a tray cover  82  which fit together to enclose power supply  86  and disk drive  88  within removable assembly  46 . Fan  90  is affixed to the rear portion of base tray  80  (and is more clearly visible in FIG.  5 ). A front bezel  84  is affixed to the front portion of base tray  80 . Bezel  84  and the front of base tray  80  have selected openings for the placement of connectors for interconnection of both power and computer data transfer signals. Bezel  84  also provides assembly points which meet with connector panel  42 . 
     FIG. 3 shows a front view of the disk drive expansion system  28  for two modules  30 . As shown, bottom module  30  rests on feet  64 . Power cable  32  is routed underneath the center portion of bottom module  30  and connects to bottom module  30  near the front, lower portion of bottom module  30 . Disk drive interface cable  26  is similarly routed beneath the center portion of bottom module  30  and connects computer  20  as shown in FIG. 1 to the lower portion of bottom module  30  as shown in FIG.  3 . Cables  36  and  38  provide power and computer signal interconnection, respectively, to interconnect bottom module  30  with the upper module  30  of FIG. 3. A set screw  100  secures the removable drive assembly  46  as shown in FIG. 1 to the case  44 . This provides additional security to prevent the removable assembly  46  from sliding out of case  44 . 
     A power switch  102  is located near the lower power feed of module  30 . In FIG. 3, a power switch  102  can be seen to the right of the interconnection of power cable  32  with lower module  30 . Power switch  102  of the upper module  30  is located to the right side of interconnection cable  36 . 
     Similarly, an address select switch  104  is located near the upper portion of module  30  in between interconnection cables  36  and  38 . Selection switch  104  is used to select the address of the particular disk drive or peripheral. Address selection is required with SCSI protocols, as well as a variety of other computer interconnection formats. The address selection switches shown in FIG. 3 both indicate address zero being selected. In actual use, it is necessary to use different addresses for each module  30  which is attached to expansion stack  28 . 
     Referring to FIG. 4, a schematic of the wiring interconnection of module  30  is shown. The physical lay out of this wiring harness assembly is shown in FIG.  5 . Incoming power is supplied to the lower connector J 1  which is wired in parallel with output power connector J 2  so that power can be routed to the next module  30 . Switch  102  connects the incoming power supply to power supply  86 . Power supply  86  converts the incoming power supply waveform, typically 110 volts AC to suitable direct current (DC) waveforms to power drive  88  and fan  90 . Selection switch  104  is connected to the address section of drive  88  and enables a user to select the address of each drive of expansion stack  28  without having to locate and select jumpers on the disk drive board. It also enables the user of a disk drive to easily set the address required without forcing the user to examine the internal workings of a module, or computer peripheral system, something which is still feared by many in this day of “computerization”. 
     A computer interconnection cable such as a SCSI interface cable is attached to connectors J 4  and J 5  as shown in FIG.  4 . Connectors J 4  and J 5  route the computer signal to disk drive  88 , and allow interconnection of one module  30  to additional modules  30  through the use of the second connector. 
     A drive activity light omitting diode (LED), D 2  is connected to drive  88 . The drive activity LED, D 2  is activated by drive  88  to indicate to a user when the drive is enabled, and data is being accessed or written. 
     Referring to FIG. 5, the relative locations of power supply  86 , fan  90 , and the connector and switch assemblies as they are mounted in base  80  is shown. Disk drive  88  is located in area  100 , and is not shown for clarity so that the wire harnesses can be more easily seen. 
     Referring now to FIG. 6, a more compact peripheral expansion unit is shown. Unlike the system shown in FIG. 1, the configuration of FIG. 6 is not expanded by stacking additional modules on top of each other as module  30  are stacked in FIG.  1 . The implementation shown in FIG. 6 includes a bottom enclosure  122  and a top enclosure  124 . A front bezel  126  is incorporated as of the front structural member as well. This differs from the configuration of removable assembly  46  in which base tray  80  include a front portion, and bezel  84  fits over the front portion of base tray  80  as shown in FIG.  2 . 
     A rear panel  128  is attached to both the lower portion  122  and upper portion  124  of the enclosure by screws  190 . A backplane  130  is located just in front of back panel  128 . Backplane  130  provides interconnection for power supply modules  132  and/or power supply module  134 . Backplane  130  also provides interconnection for several disk drives which are placed on carrier cards. These disk drives are individually identified as drives  136 ,  138 ,  140 , and  144 , but in practice are identical disk drive assemblies which may be “hard cards” or other hard disk drives which are attached to a mounting board. Power supplies  132  and  134 , as well as disk drives  136 ,  138 ,  140  and  144  slide into the lower portion of the housing  122  through channels  150  which are preferably attached to (but may be formed within) the bottom half of enclosure  122 . 
     Power supply  132  meets with connector  152  on a power interconnection board  153 . Power supply cable  166  allows this power supply assembly to be connected to a power source (such as 110 volts AC). Similarly, power supply  134  is plugged into connector  154  is located on power supply board  155 . An additional power cable (not shown) allows board  154  to be connected with a power source. In certain configurations, it may be desirable, or preferable to interconnect boards  155  and  190  so that a single power supply line  166  may be used to provide a power source for the entire system. 
     A pair of thin, high volume fans  160  are placed on either side of the enclosure, adjacent to power supplies  132  and  134 . Vent holes  162  are located in the bottom portion of enclosure  122 , and similar vent holes  164  are located in the top portion of enclosure  134 . Vent holes  162  and  164  allow air flow through enclosure  132  and  124  to allow cooling of the power supplies and disk drives. 
     Bezel  126  has two openings for each internal disk drive assembly. Each disk drive assembly includes a disk activation LED 188  and a selection switch block  178 . Activity LED 188  is visible through openings  180 ,  182 ,  184 , and  186  for disk drives  136 ,  138 ,  140 , and  144 , respectively. Similarly, switch blocks  170  are accessible through openings  170 ,  172 ,  174 , and  176  for disk drives  136 ,  138 ,  140 , and  144 , respectively. Openings  192  near the outer portion of bezel  125  provide for additional air flow through the system. Preferably, the fans  160  are oriented to expel air out of vent holes  162  and  164 . The in flow of air through openings  192 , and rear panel  128  provide air flow to cool power supplies  132  and  134 , and disk drives  136 ,  138 ,  140 , and  144 . 
     A computer interconnection cable, not shown, interconnects connectors  156  on mother board  130  with computer  20  (as shown in FIG.  1 ). This may be the aforementioned SCSI interface protocol as is employed with the modular implementation described in FIGS. 1-5. 
     In order to allow the disk drives  136 ,  138 ,  140 , and  144  to be easily mounted in the slots  150  of the bottom portion of enclosure  122 , and interconnected to mother board  130 , the disk drives are mounted on rigid carriers which may also act as disk controller boards, containing logic circuits, as well as providing mounting for LED 188  and switch  178 . 
     The physical side of the disk drives shown in FIG. 6 is smaller than the size of the disk drives  88  as shown in FIG.  2 . As a result, the disk drives shown in FIG. 6 are expected to have a lower storage capacity than disk drives  88 . By providing a modular expansion system, a user can purchase only the amount of data storage that he believes he requires, and may easily add to it in the future as his needs expand. This allows the user to build on a single investment of an expansion system, without being forced to discard the previous expansion system each time the user wishes to increase his data storage capability. There is no restriction using the present system that each drive added to the system have the same storage capacity, or storage medium. It is possible with the present system to include so called standard winchester disk drives, drives which incorporate vertical recording of magnetic patterns, as well as optical storage drives within the physical configuration of the embodiments. 
     An additional benefit of the storage technique of the present invention is the ability to distribute data storage and parity information amongst several disk drives. If three drives are employed, data can be stored on two of the drives, and parity checking information for that data stored on a third drive. As a result, if any one of the disk drives fails to operate, all of the data can be restored by accessing the remaining two drives. 
     If one of the disk drives which contains data fails, that data can be reconstructed by comparing the parity information contained on the third drive with the data contained on the other data drive in order to determine what data has been lost, and reconstructed. Similarly, if the drive containing the parity information fails to operate, the two data drives already contain all of the valid data which can be used to reconstruct the parity information. 
     This eliminates the need to continuously back up data stored on disk drives in order to ensure that the data is not lost. Additionally, this data protection system may operate with a reduced redundancy as the number of disk drives increases. Using standard back up techniques, a 100% redundancy, or full back up copy, is required. Employing three drives, with two containing data, and one containing one parity bit for every two bits of data results in a 50% decrease in data storage in order to ensure that no data is lost. If four drives are employed, three of the drives can contain data, and the fourth drive contains parity check information for the first three drives. In this configuration, the redundancy factor has been reduced to 33%. Similarly, if five disk drives were employed, data is stored on the first four, and parity information on the fifth. This results in only a 25% redundancy storage factor. As is the case for a three drive system, if one of the five disk drives was to cease functioning, data and parity information on the remaining four can be easily used to reconstruct the missing data, or parity information which was lost. 
     This technique can be employed as additional disk drives are added to the system. If a system is initially operating with three disk drive, and a fourth is added, the storage protocol of the host computer in one embodiment will change and adapt to a four disk drive system including data storage on three drives and parity information on the fourth. For that information which was only stored on the first three drives which were present in the system, the host computer will only look to those three drives for data and parity information. 
     In another embodiment, the system will always store data onto disk drives, and parity information and a third. Adding a fourth drive to the system causes the host computer to distribute the data differently, writing data on two of the disk drives, and parity information on a third. The host system will attempt to evenly distribute the added information to ensure that the three disk drives which were originally in the system will not become filled to capacity while the added disk drive remains essentially empty. In this embodiment, once information which was previously stored on the three disk drives in the system is modified, or added to, the files are rewritten by the host computer in order to distribute the data amongst the four disk drives presently in the system. The same principles apply when a fifth, sixth, seventh or subsequent disk drive is added to the system. 
     There has been described here and above a novel expandable disk drive system. Those skilled in the art may now make numerous departures from the particular embodiments disclosed here and above, including, but not limited to enclosing two, three, or more discreet disk drives within each module  30  of the system; employing 5¼ inch 3½ inch, 1.8 inch, 1 inch, or other varieties of form factor disk drives; employing numerous types of data protocols; employing optical or worn drives; employing larger or smaller power supplies within each module; employing piezo electric or semiconductor based cooling systems instead of fans; reducing the number of fans within the stack and allowing air to flow between modules of the stack; varying the type of connectors, switches, screws, nuts and bolts which are employed; varying the number of data lines which are interconnected between the adjacent modules or the host computer system; employing different switch assemblies, additional or fewer indicator lamps; employing liquid crystal displays instead of light emitting diodes; providing active buffer or circuitry to electrically isolate the stack; employing a/c powered fans; and making numerous other modifications of the implementations described above without departing from the inventive spirit herein which is defined solely by the following claims.