Patent Publication Number: US-7710718-B2

Title: Method and apparatus for enforcing of power control in a blade center chassis

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   The present application is a continuation application of pending U.S. patent application Ser. No. 11/209,868, which was filed on Aug. 23, 2005, which is assigned to the assignee of the present invention. The present application claims priority benefits to U.S. patent application Ser. No. 11/209,868. 

   TECHNICAL FIELD 
   The present invention relates in general to data processing systems, and in particular, to communications network devices referred to as blade servers. 
   BACKGROUND INFORMATION 
   The use of servers as devices within communications networks is well known in the art. A server is equipment that makes available file, database, printing, facsimile, communications or other services to client terminals/stations with access to the network the server serves. When the server permits client/terminal station access to external communications network it is sometimes known as a gateway Servers are available in different sizes, shapes and varieties. Servers may be distributed throughout a network or they may be concentrated in centralized data centers. 
   Advances in centralized data processing centers have resulted in smaller form factors for server devices and an increase in the density of processing units, thereby reducing space requirements for computing infrastructure. One common form factor has been termed in the art a “blade server,” comprising a device built for vertically inserting into a chassis that can house multiple devices that share power and other connections over a common backplane, i.e., a blade center. Slim, hot swappable blade servers (also referred to herein as “blades”) fit in a single chassis like books in a bookshelf—and each is an independent server, with its own processors, memory, storage, network controllers, operating system and applications. The blade server slides into a bay in the chassis and plugs into a mid- or backplane, sharing power, fans, floppy drives, switches, and ports with other blade servers. The benefits of the blade approach will be readily apparent to anyone tasked with running down hundreds of cables strung through racks just to add and remove servers. With switches and power units shared, precious space is freed up—and blade servers enable higher density with far greater ease. With a large number of high-performance server blades in a single chassis, blade technology achieves high levels of density. 
   Even though power consumption and device complexity per unit of processing power may actually decrease with a blade center, since the physical density of the computing devices has increased, the demands on power consumption for processing power and cooling have also intensified as overall computing power has increased. A blade center chassis has resources such as power and cooling that are shared by multiple components in the enclosure. A management module is present in each chassis which is responsible for managing all components within a chassis and the relationship between them. Each blade is allocated a fixed amount of power or cooling capacity. If any blade exceeds its allocation, it can force the entire chassis to exceed threshold values, which can, in turn, force the common power supply to shut down, causing other blades to be turned off. Another risk is that any blade exceeding its allocation can cause other blades to shut down due to temperatures exceeding their critical thresholds. 
   Probably, one of the most pressing problems associated with servers is manageability and particularly manageability as applied to chassis mounted servers. One aspect of manageability within this type of server relates to allocating power resources, which has been solved by system architecture in past configurations. Service processors on blades are required to ask the management module for permission to power on and to shut down when requested by the management module. In such a configuration, the blade server continues to maintain control over its own power consumption. In past system architectures, this feature has been preserved so that blade servers can continue to operate in an environment where the management module is not present. While past architectures have thusly addressed the majority of cases, they have not addressed the case where a blade server malfunctions, i.e., does not properly respond to the directives of the management module. Therefore, past blade center system architectures have been susceptible to the malfunction of a single blade that does not follow the required protocol for power management, for example, by choosing to power on in inappropriate situations, thereby jeopardizing the operation of other blades in the chassis. 
   In view of the above problems a more reliable system and method is needed to enforce power control in a blade center chassis to prevent overloading of power and cooling resources due to a non-compliant, malfunctioning blade server. 
   SUMMARY OF THE INVENTION 
   The present invention addresses the foregoing need by providing a mechanism for changing ownership over the physical power to the blade. When a management module is present, it will maintain control over the power to the blade. When the management module is not present, control over power to the blade is switched to the service processor on the blade. This arbitration of control over power to a blade is accomplished by implementing a watchdog timer mechanism between the management module and the switch controlling power to the blade. The management module is responsible for tickling, i.e., continuously triggering at discrete intervals, the watchdog timer when the management module is present in the chassis and is operating normally. This mechanism provides the management module with control over power. If the management module malfunctions or is removed, control over power is switched to the local service processor as soon as the watchdog timer is not tickled by the management module. 
   An object of the present invention is to provide a mechanism for controlling the power to a blade server in a blade center, whereby the control of the power is retained by a management module when present in the blade center chassis. 
   Another object of the present invention is to prevent blade servers that malfunction or that are defective and thus, do not adhere to the architecture protocol for power control from powering on in a blade center chassis. 
   Another object of the present invention is to force malfunctioning blade servers to power off when directed by the management module. 
   Thus, another object of the present invention is to protect blade servers in a blade center chassis from the adverse effects of a malfunctioning or defective blade server, such as total loss of power in the blade center chassis due to overloading the common power supply or from exposure to excessive thermal loading. 
   Still another object of the present invention is to provide for the secure and reliable operation of blade servers in a blade center chassis by providing fault-tolerance for the adverse effects of a malfunctioning or defective blade server, such as overloading the common power supply or excessive thermal loading. 
   Another object of the present invention is to provide a means whereby power can be individually switched to blades occupying the slots of a blade center chassis. 
   Yet another object of the present invention is to provide a watchdog timer mechanism that can revert control over power switching to an individual blade server when the management module is not present or does not respond when queried. 
   The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
       FIG. 1  illustrates a prior art embodiment of system components in a blade center. 
       FIG. 2  illustrates system components in one embodiment of the present invention. 
       FIG. 3  illustrates system components in one embodiment of the present invention. 
       FIG. 4  is a flow chart of a prior art power cycle process. 
       FIG. 5  is a flow chart of a power on portion of a power cycle process in one embodiment of the present invention. 
       FIG. 6  is a flow chart of a power off portion of a power cycle process in one embodiment of the present invention. 
       FIG. 7  illustrates a schematic diagram of a blade center management subsystem. 
       FIG. 8  illustrates a front, top and right side exploded perspective view of a blade center chassis in accordance with an embodiment of the present invention. 
       FIG. 9  illustrates a rear, top and left side perspective view of the rear portion of a blade center chassis in accordance with an embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
   In the following description, numerous specific details are set forth such as specific word or byte lengths, etc. to provide a thorough understanding of the present invention. However, it will be obvious to those skilled in the art that the present invention may be practiced without such specific details. In other instances, well-known circuits have been shown in block diagram form in order not to obscure the present invention in unnecessary detail. For the most part, details concerning timing considerations and the like have been omitted inasmuch as such details are not necessary to obtain a complete understanding of the present invention and are within the skills of persons of ordinary skill in the relevant art. 
   Refer now to the drawings wherein depicted elements are not necessarily shown to scale and wherein like or similar elements are designated by the same reference numeral through the several views. 
   The prior art system components and architecture for controlling power in a blade center chassis are illustrated in  FIGS. 1 and 4  respectively. Referring to  FIG. 1 , a blade center chassis  100  contains the following components relevant for controlling power: blade servers  130  which reside in the chassis slots  120 ; management modules (MM)  110  which may contain their own MM processor  117 ; a common power supply  140  and ventilators  150 ; and communication interfaces between these components  125 ,  141 ,  151 ,  131 . In a typical prior art system, the service processor (SP)  135  on a blade  130  is required to ask, via the bidirectional interface  125 , the MM processor  117  on the MM  110  for permission to power on and to shut down when requested by the MM  110 . In this architecture, the common power supply  140  is routed via the power bus  145  to all slots  120  in the chassis  100 . There is no mechanism for the MM  110  to directly constrain power to an individual blade  130 . The MM  110  controls the common power supply  140  via bus  141  and the ventilator  150  via a fan bus  151 . The bidirectional interface  125  between the MM processor  117  and the SP  135 , may be a multi-drop RS-485 interface. Other interface protocols for  125  may be implemented. The control buses  141 ,  151 ,  131  may be I 2 C interfaces. 
   In  FIG. 4 , the operation of the prior art system in  FIG. 1  is illustrated with an example of a power on process  410  and a power off process  450  for a server blade  130  in a chassis slot  120  of a blade center chassis  100 . In the power on process  410 , no action is taken until a blade  130  is present  411 . If no MM  110  is present  412 , the blade  130  powers on  416  without external control. If an MM  110  is present, then the blade  130  is required to request permission  413  from the MM  110  to power on. The MM  110  is responsible for deciding  414  if the blade  130  can power on. The MM  110  will follow whatever rules are in effect that determine whether the power operation should proceed. If the MM  110  decides to deny the power on request, the blade  130  may repeat the request  413  in a timely manner for reconsideration. If the MM  110  allows the power on request  413 , the MM  110  issues a power on command  415  to the blade  130 , upon which the blade is permitted to power on  416 . 
   Noteworthy in the prior art case is that the blade  130  remains in physical and logical control of the power on  416 , which is executed by the SP  135  issuing a command on the bus  131  for the switch module  132  to switch on power  145  from the common power supply  140  to the blade  130 . Physical control refers to controlling the actuator stage providing electrical power connections, for example, providing current to a relay coil that closes a power relay switch. Logical control refers to issuing the command to activate power connections, thereby controlling the policy and the timing of the decision to supply power. In one example, logical control may be asserted with a digital control signal, such as a static 12V DC digital output. In another embodiment, logical control may be primarily asserted by sending a binary command to a control unit, which then executes further logical control in direct response to the binary command. In further examples, the binary command may be sent bitwise in parallel or serially, using an appropriate interface and driver. Important to note is that logical control may be transferred with logic circuitry or by circuitry responsive to software commands. Transfer of physical control will generally involve rerouting a control path for switching electrical power. 
   Also important is that in this prior art architecture, the blade  130  may malfunction and ignore the commands via interface  125  from the MM  110 ,  117  or may violate the architecture protocol  410  at any time. Such an error mode presents significant risks for the other blades in the chassis, particularly for the case of a malfunctioning blade  130  powering on  416 . This kind of non-compliance by a blade can cause the power consumption to exceed threshold values, which can cause loss of power to the entire blade center chassis  100 . Alternatively, a malfunctioning blade can cause other blades to shut down due to temperatures exceeding their threshold values. The efforts of the MM  110  to maintain power and temperature in the blade chassis  100  within threshold values may be therefore undermined by a single malfunctioning blade  130 . 
   A prior art power off process is illustrated in  450 . If no MM is present  451  then the blade may directly switch off  454  at any time. If the MM is present  451 , the system stays in the power on state until the MM decides  452  to issue a power off command  453 . In other examples, the MM may respond to external input, such as a power switch or shut down command, in deciding to power off  452 . Once the blade has received the power off command  453  from the MM, it must switch itself off  454 . Note that the malfunctioning of a blade  130  in this case  450  may be the refusal to power off  453 , which carries all the same negative implications for resource management mentioned above for case  410 . Since the MM processor  117  does not have physical control over the circuitry for switching power to the blade  132  or logical control over the SP  135 , the efforts of the MM  110  for managing power and temperature are also undermined by a malfunctioning blade  130  when it refuses to power off  454 . 
   The present invention provides a mechanism for changing ownership over the physical power to the blade. In  FIG. 2 , a hardware configuration of an embodiment of the present invention is illustrated. The SP  235  on the blade  230  maintains an interface  231  to a switch module  232  on the blade server  230 . However, the power bus interface  222  from the blade  230  is routed through an additional control switch  225  located on a chassis slot  220  modified for this purpose. Each chassis slot  220  in the chassis  200  contains an additional switch module  225  for individually switching power  221  from the common power supply  240  to a blade  230 . The SP  235  communicates with the MM processor  217  via the interface  226 . A modified MM  210  contains a watchdog timer module  215 , which may be tickled via bus  212  by the MM processor  217 . The watchdog timer  215  may assert control of the chassis slot control switch  225  via bus interface  211 . If for any reason the MM  210  does not respond or is not present, the watchdog timer  215  releases control of switch  225 , in one example by closing the switch, while concurrently a timeout in interface  226  is registered by SP  235 , which responds by reasserting local control over switch  232  via interface  231 . Noteworthy in the hardware configuration of  FIG. 2  is that the blade  230  can be forced to comply with the decisions of the MM  210  in its efforts to manage power and temperature in the chassis  200 , leaving no possibility of a blade  330  malfunctioning and endangering the other equipment in the chassis  200 . 
   In  FIG. 3 , an alternative embodiment of a hardware configuration of the present invention is illustrated. The SP  335  on the blade  330  maintains an interface  331  to a switch module  325  in the chassis slot  320 , which has been modified accordingly. The power bus interface  322  from the blade  330  is routed directly through a control switch  325 ; blade  330  no longer requires its own power switching circuitry. Each chassis slot  320  in the chassis  300  contains a switch module  325  for individually switching power  321  from the common power supply  340  directly to a blade  330 . The SP  335  communicates with the MM processor  317  via the interface  326 . A modified MM  310  contains a watchdog timer module  315 , which may be tickled via bus  312  by the MM processor  317 . The watchdog timer  315  may assert control of the chassis slot control switch  325  via bus interface  311 . If for any reason the MM does not respond or is not present, the watchdog timer  315  releases control of switch  325 , while concurrently a timeout in interface  326  is registered by SP  335 , which responds by reasserting control over switch  325  via interface  331 . Noteworthy in the hardware configuration of  FIG. 3  is that the blade  330  can be forced to comply with the decisions of the MM  310  in its efforts to manage power and temperature in the chassis  300 , leaving no possibility of a blade  330  malfunctioning and endangering the other equipment in the chassis  300 . 
     FIG. 5  illustrates a power on portion  510  of a power cycle process in one embodiment of the present invention. When a MM  210 ,  310  is present, it will assert control  513  over the power  221  to the blade  230 ,  330 . In one example MM  210  asserts control by commanding the SP  235  via interface  226  not to operate switch  232 . In another example, the MM  310  asserts control by commanding the SP  335  via interface  326  not to operate switch  325  and through watchdog timer  315 , which enforces control of  325  via interface  311 . In another example, the MM  210  asserts control by forcing switch  232  to close while switch  225  is initially open. Other mechanisms for asserting physical or logical control over power to the blade may by MM  210  or  310  may be practiced in embodiments of the present invention. After asserting control, the MM processor  217 ,  317  begins tickling  514  the watchdog timer  215 ,  315  via interface  212 ,  312 . Tickling involves sending trigger pulses or messages with a predefined interval to the watchdog timer  215 ,  315 . Other configurations of the watchdog timer  215 ,  315  may be practiced within the scope of the present invention, such as direct monitoring of communication  226 ,  326 , or installing the watchdog timer  215 ,  315  on the chassis slot  220 ,  320 . While the watchdog timer  215 ,  315  is tickled, the blade  230 ,  330  may request  515  power on from the MM  210 ,  310 . The MM  210 ,  310  may decide  516  to power on the blade  230 ,  330 , and then, in one example of the present invention, switches power on  517  via switch module  225 ,  325 . The MM may decide not  516  to power on the blade  230 ,  330 , and as long as the MM  210 ,  310  is alive and responding  518 , the blade may continue to issue another power on request  515 , since the blade  230 ,  330  does not have control over the power switch  225 ,  325  as long as the watchdog timer  215 ,  315  is tickled. If the MM  210 ,  310  stops  518  tickling the watchdog timer  215 ,  315 , the watchdog timer  215 ,  315  resets control  519  to the power switch  225 ,  325  via bus  211 ,  311  to the SP  235 ,  335 . At such time, the blade  230 ,  330  may then switch power on  520 . 
     FIG. 6  illustrates a power off portion  610  of a power cycle process in one embodiment of the present invention. Note that the power on state may be attained either under control of the MM  210 ,  310 , in which case  503  represents the continuation path of the process, or under control of the SP  235 ,  335 , in which case  504  represents the continuation path of the process. If the blade  230 ,  330  was powered on  520  by the SP  235 ,  335 , via  504 , then if the MM  210 ,  310  is inserted  611 , the MM  210 ,  310  asserts control  513  and begins tickling  514  the watchdog timer  215 ,  315 . If the MM  210 ,  310  is not inserted, then the control remains with the SP  235 ,  335 , and the blade  230 ,  330  may switch itself off  614 . If the MM  210 ,  310  is present and is tickling the watchdog timer  215 ,  315 , path  503  represents the power on state of the blade  230 ,  300  until the blade issues a power off request  616 . If the MM  210 ,  310  decides to power off  613  the blade  230 ,  330 , then the MM  210 ,  310  may power off  613  the blade by opening switch  225 ,  325  and interrupting the power bus  221  to the blade&#39;s chassis slot  220 ,  320 . Other subsidiary mechanisms for executing the power off  613  may be implemented in other embodiments of the present invention, such as instructing SP  235  to physically power off switch  232  via bus  231  or instructing SP  335  to physically power off switch  325  via bus  331 . However, the MM  210 ,  310  always maintains overriding physical and logical control of switch  225 ,  325  to enforce power policy in case the blade  230 ,  330  malfunctions. If the MM  210 ,  310  decides not  612  to power off the blade  230 ,  330  and the MM  210 ,  310  continues to tickle the watchdog timer  615 , the blade has no other option but to issue another request to power off. If the MM  210 ,  310  stops  615  tickling the watchdog timer  215 ,  315 , the watchdog timer  215 ,  315  resets control  519  to the power switch  225 ,  325  via bus  211 ,  311  to the SP  235 ,  335 . At such time the blade  230 ,  330  may then switch power off  614 . In the power off state, a remedial power supply sufficient for operating the SP  235 ,  335  and other necessary control circuitry on the blade  230 ,  330  is not precluded by the chassis slot  220 ,  320 . 
     FIG. 7  is a schematic diagram of a blade center chassis management subsystem, showing engineering details of the individual management modules MM 1 -MM 4 , previously represented schematically by MM  210 ,  310 , and showing engineering details of the individual components contained in previous schematic representations of blade center chassis  200 ,  300 . Referring to this figure, each management module has a separate Ethernet link to each one of the switch modules SM 1  through SM 4 . Thus, management module MM 1  is linked to switch modules SM 1  through SM 4  via Ethernet links MM 1 -ENet 1  through MM 1 -ENet 4 , and management module MM 2  is linked to the switch modules via Ethernet links MM 2 -ENet 1  through MM 2 -ENet 4 . In addition, the management modules are also coupled to the switch modules via two well known serial I 2 C buses SM-I 2 C-BusA and SM-I 2 C-BusB, which provide for “out-of-band” communication between the management modules and the switch modules. Similarly, the management modules are also coupled to the power modules (previously represented schematically by  240 ,  340 ) PM 1  through PM 4  via two serial I 2 C buses (corresponding to interfaces  241 ,  341 ) PM-I 2 C-BusA and PM-I 2 C-BusB. Two more I 2 C buses Panel-I 2 C-BusA and Panel-I 2 C-BusB are coupled to media tray MT and the rear panel. Blowers BL 1  and BL 2  (previously represented schematically by  250 ,  350 ) are controlled over separate serial buses Fan 1  and Fan 2  (corresponding to interfaces  251 ,  351 ). Two well known RS485 serial buses RS485-A and RS485-B (corresponding to interfaces  226 ,  326 ) are coupled to server blades PB 1  through PB 14  for “out-of-band” communication between the management modules and the server blades. 
     FIG. 8  illustrates a front, top and right side exploded perspective view of a server blade system, showing engineering details of the individual components contained in previous schematic representations of blade center chassis  200 ,  300 . Referring to this figure, main chassis CH 1  houses all the components of the server blade system. Up to 14 processor blades PB 1  through PB 14  (or other blades, such as storage blades) are hot pluggable into the 14 slots in the front of chassis CH 1 . The term “server blade”, “blade server”, “processor blade”, or simply “blade” is used throughout the specification and claims, but it should be understood that these terms are not limited to blades that only perform “processor” or “server” functions, but also include blades that perform other functions, such as storage blades, which typically include hard disk drives and whose primary function is data storage. 
   Processor blades provide the processor, memory, hard disk storage and firmware of an industry standard server. In addition, they include keyboard, video and mouse (“KVM”) selection via a control panel, an onboard service processor, and access to the floppy and CD-ROM drives in the media tray. A daughter card may be connected via an onboard PCI-X interface and is used to provide additional high-speed links to various modules. Each processor blade also has a front panel with 5 LED&#39;s to indicate current status, plus four push-button switches for power on/off, selection of processor blade, reset, and NMI for core dumps for local control. 
   Blades may be “hot swapped” without affecting the operation of other blades in the system. A server blade is typically implemented as a single slot card (394 mm×227 mm); however, in some cases a single processor blade may require two slots. A processor blade can use any microprocessor technology as long as it is compliant with the mechanical and electrical interfaces, and the power and cooling requirements of the server blade system. 
   For redundancy, processor blades have two signal and power connectors; one connected to the upper connector of the corresponding slot of midplane MP (described below), and the other connected to the corresponding lower connector of the midplane. Processor Blades interface with other components in the server blade system via midplane interfaces comprising: 1) Gigabit Ethernet; 2) Fiber Channel; 3) management module serial link; 4) VGA analog video link; 4) keyboard/mouse USB link; 5) CD-ROM and floppy disk drive (“FDD”) USB link; 6) 12 VDC power; and 7) miscellaneous control signals. These interfaces provide the ability to communicate with other components in the server blade system such as management modules, switch modules, the CD-ROM and the FDD. These interfaces are duplicated on the midplane to provide redundancy. A processor blade typically supports booting from the media tray CDROM or FDD, the network (Fiber channel or Ethernet), or its local hard disk drive. 
   A media tray MT includes a floppy disk drive and a CD-ROM drive that can be coupled to any one of the 14 blades. The media tray also houses an interface board on which is mounted interface LED&#39;s, a thermistor for measuring inlet air temperature, and a 4-port USB controller hub. System level interface controls consist of power, location, over temperature, information, and general fault LED&#39;s and a USB port. 
   Midplane circuit board MP is positioned approximately in the middle of chassis CH 1  and includes two rows of connectors; the top row including connectors MPC-S 1 -R 1  through MPC-S 14 -R 1 , and the bottom row including connectors MPC-S 1 -R 2  through MPC-S 14 -R 2 . Thus, each one of the  14  slots includes one pair of midplane connectors located one above the other (e.g., connectors MPC-S 1 -R 1  and MPC-S 1 -R 2 ) and each pair of midplane connectors mates to a pair of connectors at the rear edge of each processor blade (not visible in  FIG. 8 ). 
     FIG. 9  is a rear, top and left side perspective view of the rear portion of the server blade system. Referring to  FIGS. 8 and 9 , a chassis CH 2  houses various hot pluggable components for cooling, power, control and switching. Chassis CH 2  slides and latches into the rear of main chassis CH 1 . 
   Two hot pluggable blowers BL 1  and BL 2  (previously represented schematically by  250 ,  350 ) include backward-curved impeller blowers and provide redundant cooling to the server blade system components. Airflow is from the front to the rear of chassis CH 1 . Each of the processor blades PB 1  through PB 14  includes a front grille to admit air, and low-profile vapor chamber based heat sinks are used to cool the processors within the blades. Total airflow through the system chassis is about 300 CFM at 0.7 inches H 2 O static pressure drop. In the event of blower failure or removal, the speed of the remaining blower automatically increases to maintain the required air flow until the replacement unit is installed. Blower speed control is also controlled via a thermistor that constantly monitors inlet air temperature. The temperature of the server blade system components are also monitored and blower speed will increase automatically in response to rising temperature levels as reported by the various temperature sensors. 
   Four hot pluggable power modules PM 1  through PM 4  (previously represented schematically by  240 ,  340 ) provide DC operating voltages for the processor blades and other components. One pair of power modules provides power to all the management modules and switch modules, plus any blades that are plugged into slots  1 - 6 . The other pair of power modules provides power to any blades in slots  7 - 14 . Within each pair of power modules, one power module acts as a backup for the other in the event the first power module fails or is removed. Thus, a minimum of two active power modules are required to power a fully featured and configured chassis loaded with 14 processor blades, 4 switch modules, 2 blowers, and 2 management modules  210 . However, four power modules are needed to provide full redundancy and backup capability. The power modules are designed for operation between an AC input voltage range of 200 VAC to 240 VAC at 50/60 Hz and use an IEC320 C14 male appliance coupler. The power modules provide +12 VDC output to the midplane from which all server blade system components get their power. Two +12 VDC midplane power buses are used for redundancy and active current sharing of the output load between redundant power modules is performed. 
   Management modules MM 1  through MM 4  (previously represented schematically by  210 ,  310 ) are hot-pluggable components that provide basic management functions such as controlling, monitoring, alerting, restarting and diagnostics. Referring to  FIGS. 2 and 3 , the management modules  210 ,  310  contain the MM Processor  217 ,  317  and the watchdog timer  215 ,  315  with its interface  211 ,  311  to the individual switch module  225 ,  325  in embodiments of the present invention. Management modules also provide other functions required to manage shared resources, such as the ability to switch the common keyboard, video, and mouse signals among processor blades. 
   Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.