Patent Document

FIELD OF THE INVENTION 
     This invention relates generally to the field of storage and more particularly to a method and apparatus for providing scalable data storage. 
     BACKGROUND OF THE INVENTION 
     As is known in the art, Network Attached Storage (NAS) is a data storage mechanism that allows a host device to access storage devices using an Internet Protocol (IP) network. NAS devices are generally file servers that are referenced using IP addresses and are coupled to storage media, such as a RAID array or the like. The NAS therefore serves as a gateway between the storage media and the network. One example of the use of NAS can be found in the Celerra NS600 Network Server, from EMC Corporation of Hopkinton Mass. which includes a front end NAS enclosure and a back end Clariion storage enclosure. 
     One advantage of the NAS structure is that it enables data storage, data security and data management to be centralized in an environment with many servers running different operating systems. In addition, the use of a NAS-based system such as the Celerra system from EMC is a simple and straightforward way for a host to expand its storage capacity through the use of existing IP host functionality. 
     Although NAS-based systems are useful, to provide consistent, high performance client support, businesses typically rely on high availability systems. In the prior art, high availability characteristics have been added to a NAS system by duplicating the data mover front end enclosure. For example, a block diagram of an exemplary NAS architecture  10  with some high availability characteristics is shown in  FIG. 1 . The NAS  10  includes a pair of data mover enclosures  16   a  and  16   b  which control the movement of data to and from the attached storage device (not shown). In the example of  FIG. 1 , each data mover enclosure is shown to include two data movers, which together provide some level of high availability to the overall NAS by enabling continued data mover operation in the event of a single point of failure. A control station  12  is used to monitor the operating status of the data movers. A switch is disposed between the control station  12  and the data mover enclosures  16   a  and  16   b  for forwarding control information between the control station and the data movers. Data that is read from or written to the data storage device is forwarded to and from the data movers via an External Local Area Network (LAN), not shown. 
     Although the NAS architecture  10  provides some level of high availability, because the architecture uses only a single switch and control station, a single point of failure can cause the control system to fail, and therefore the system may not have the required rate of reliability. 
       FIG. 2  shows an exemplary high availability NAS architecture which overcomes single point of failure issues. The high-availability NAS  20  includes two control stations  12  and  22  coupled via two switches to the two data mover enclosures  16   a  and  16   b . In the event of a single point of failure at any of the components, the remaining component can cover for the failed component while it is repaired. 
     The solution of  FIG. 2  is thus capable of providing high availability support in a NAS environment. One particular problem with such an arrangement, however, involves the physical connections between the individual components of the system. Each line in  FIG. 2  that connects one component to another component represents a connection between the components, such as an Ethernet cable. As the components are doubled, the number of cables is linearly increased to ensure that all necessary connections for supporting the high availability system can be maintained. For example, the four cables that were previously used to couple the data movers to the switch are increased to eight cables. The sheer number of cables that would need to fit within the enclosure makes such an arrangement undesirable, and makes any further scaling of the design prohibitive. 
     Referring briefly to  FIG. 3 , a diagram of the exemplary NAS enclosure system of  FIG. 2  is shown illustrating the clutter of cables within the enclosure, including Ethernet cables from the switches  14  and  24  to the components, and control cables (for example RS485 control cables) from the control stations  12  and  22  to the components. 
     SUMMARY OF THE INVENTION 
     The present invention includes a number of data mover devices coupled to a control station wherein each data mover has a network switch incorporated into the data mover structure. In order to control the power supplied to the data mover, the data mover includes a power control portion thereof that is always supplied with power. This “always on” power control portion of the data mover includes the associated switch, a microcontroller and a power control device. Upon receiving a command through the switch from the control station to power down the data mover, the microcontroller sends a command to the power control device, which disables the voltage regulators that supply power to the CPU and I/O logic that make up the data mover. Likewise, upon receiving a command from the control station to power up the data mover, the microcontroller instructs the power control device to enable the voltage regulators that supply power to the CPU and I/O logic that make up the data mover. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features of the invention will become more readily apparent from the following detailed description when read together with the accompanying drawings, in which: 
         FIG. 1  is a block diagram of an exemplary Network Attached Storage (NAS) system; 
         FIG. 2  and  FIG. 3  are a block diagram and enclosure diagram, respectively, provided for illustrating connectivity issues involved in modifying the NAS of  FIG. 1  to provide high availability reliability; 
         FIG. 4  is a block diagram illustrating a scalable, high availability NAS of the present invention; 
         FIG. 5  is a block diagram illustrating another embodiment of a scalable, high availability NAS of the present invention; and 
         FIG. 6  illustrates an alternative view of the NAS of  FIG. 4 , showing a top-down view of two of the data movers. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to  FIG. 4 , a diagram illustrating one embodiment of a high availability Network Attached Storage (NAS) architecture  30  according to the present invention is shown. The NAS architecture  30  is shown to include a control station  32 . The control station includes logic having functionality for retrieving operating status information from each coupled file server, or data mover. In one embodiment, the operating status information includes, among other items, information regarding the operational status of the operating system software running on each data mover and the availability of each data mover. 
     The control station  32  includes an interface card  40 , which is, for example, a Peripheral Component Interconnect (PCI) card, having a number of ports  41 ,  42  and  43 . Communication methods that are used by the control station to transfer data using the PCI card are well known in the art. The particular ports of the PCI card are described in more detail below. 
     Coupled the control station  32  are data movers DM A, DM B, DM C and DM D. The data movers may be, for example, front end data moving enclosures provided in the Celerra line of products by EMC Corporation. The data movers serve to retrieve data from a coupled storage device (not shown), and therefore provide, among other functions, file server, data management and data integrity functionality. It should be noted that, although the particular embodiment is discussed with regard to data movers, the present invention is equally applicable to any processing device that is used to transfer data, and thus the present invention is not limited to any particular implementation of the enclosure. 
     The present invention distributes the switching functionality of the prior art onto the individual data movers DM A, DM B, DM C and DM D to form a single field replaceable unit, or “FRU”. Thus, integrated into each data mover DM A, DM B, DM C and DM D is a switch, shown at  56  in  FIG. 6  and a port device  50   a ,  50   b ,  50   c  and  50   d , respectively. By providing a switch  56  in each data mover, access to the data movers by the control station  32  can be assured even in the event of a single point of failure at one switch. Thus, the on-board switch  56  in each data mover insures that high availability reliability can be met. 
     Each switch  56  is used to chain together the data movers to enable communication between the control station  32  and the data movers with a minimal amount of cabling overhead. Each port device  50   a ,  50   b ,  50   c  and  50   d  includes a downstream input port  52  for receiving data from an upstream device and inputting it to the associated switch, and an upstream output port  54  for forwarding data to the switch of a coupled downstream device. Downstream input port  52  and upstream output port  54  are preferably RJ-45 sockets coupled to the air dam (not shown) of the data mover. For the purposes of this description, the upstream direction is towards the control station  32 , and the downstream direction is away from the control station  32 . 
     Referring again to the control station  32 , the interface card  40  of the control station is shown to include three ports  41 ,  42  and  43 . In one embodiment of the invention, the three ports include two redundant networking ports  42  and  43  and a heartbeat LAN port  41 . The two networking ports  42  and  43  provide high availability accessibility to the data moving enclosures by the control station  32  through two networks. As shown in  FIG. 4 , networking port  43  connects a LAN Network A to data movers DM A and DM C through cables  46   a  and  46   b , respectively, and networking port  42  connects a LAN Network B to data movers DM B and DM D through cables  48   a  and  48   b , respectively. In the event of a failure at one of the ports  42  or  43 , access to the data movers by the control station may still be achieved using the alternate port. As is described below with reference to  FIG. 6 , each data mover is accessible to every other data mover, either through their switches  56  or through a midplane connection. 
     In the NAS architecture  30  of  FIG. 4 , only one control station  32  operates to gather the operation status information at any given time. A redundant control station  33 , shown in the NAS architecture  34  in  FIG. 5 , may be utilized to monitor the operational status of the operating control station  32  using the heartbeat LAN connection  47 , between heartbeat LAN port  41  of control station  32  and heartbeat LAN port  81  of control station  81 . Control station  32  periodically issues a pulse, or heartbeat, to indicate its operating status. In the event of the failure of the operating control station  32 , the redundant control station  33  detects the loss of heartbeat, and can signal the failure and take over control station operation. As shown in  FIG. 5 , Network A is coupled to upstream port  54   c  of data mover DM C from Network A port  83  via cable  49   a  and Network B is coupled to upstream port  54   d  of data mover DM D from Network B port  82  via cable  49   b.    
     In one embodiment of the invention, the amount of cabling between enclosures is further reduced by forwarding RS485 signals on unused signal lines of the Ethernet cable. Thus each networking port such as port  42  is capable of communicating both 100 Mbit Ethernet signals and serial RS485 signals. Such an embodiment could be implemented in a system wherein 1 Gigabit Ethernet cabling is used, but communication is only performed between the enclosures at a 100 Mbit rate. In such a configuration, as described in the IEEE standard 802.3z, incorporated herein by reference, two of the signal wires are unused. In one embodiment of the invention, the control station includes logic to overlay the RS485 signals on the unused Ethernet signal wires, thereby further reducing by half the cabling and switching logic illustrated in  FIG. 4 . 
       FIG. 4  illustrates an NAS system and architecture that is highly flexible; by distributing the switching functionality to the individual data movers, data movers may be added indefinitely to achieve increased storage, performance or reliability without physical constraints. 
       FIG. 6  is a schematic block diagram showing a “top down” view of data movers DM A and DM B, showing internal components and their connection to each other through a midplane  60 . As shown in  FIG. 6 , each data mover includes its port device  50 , a switch  56 , a microcontroller μC  62 , a power controller or PIC  64 , voltage regulators  66 , one or more CPUs, I/O logic  68  and a pair of addressing devices, MAC A  70  and MAC B  72 . All of these components are formed on a single board to form a FRU. 
     In one embodiment of the invention, switch  56  is a model BCM5325 switch from Broadcom Corporation of Irvine, Calif. However, it will be understood that any switch that operates in a compatible manner may be utilized. The voltage regulators  66  operate to provide power to the CPUs and I/O logic  68  and addressing devices, MAC A  70  and MAC B  72 . While not all connections between the components in each data mover are shown, one of ordinary skill in the art will know the interconnections between the elements that are not shown. 
     Commands from the control station  32  input to data mover DM A at switch  56   a  can be communicated to the microcontroller  62   a , MAC A  70   a  and, through the midplane  60 , to MAC A  72   b . Likewise, commands from the control station  32  input to data mover DM B at switch  56   b  can be communicated to the microcontroller  62   b , MAC B  70   b  and, through the midplane  60 , to MAC B  72   a.    
     On occasion, it is desirable for a data mover to be powered down, for example, for maintenance or replacement. Likewise, a data mover in a NAS system may be used as a back-up device that must be powered up when needed. When a data mover is to be powered down, the control station  32  sends a power down command to the data mover through its associated network cable and port  50 . Switch  56  forwards the command to the microcontroller  62 , which sends the power down command to the PIC  64 . Upon receiving the power down command from the microcontroller  62 , PIC  64  sends a disable signal to the voltage regulators  66  that provide power to the remainder of the data mover, including the CPU and I/O logic  68  and the MACs  70  and  72 , thus powering down the data mover. 
     However, because the switch  56  must be powered to receive commands from the control station  32  when the data mover is in a powered down state, the switch  56 , microcontroller  62  and PIC  64  are not powered by voltage regulator  66 , but are powered by a different voltage regulator (not shown) which always provides power to these components. As shown in  FIG. 6 , these components are mounted in an “always on” portion  74  of the data mover and thus receive power regardless of the on or off state of the data mover. 
     Accordingly, the present invention incorporates switches onto each data mover in order to create a single field replaceable unit, or “FRU”, that contains the functionality of the data mover along with the switching function that was previously handled on a separate board. To enable the switch portion of the FRU to process power up and power down commands from the control station, the switch, microcontroller and PIC are separately powered and are in an “always on” state. 
     The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of the equivalency of the claims are therefore intended to be embraced therein.

Technology Category: 4