Abstract: In part, the invention relates to a system and method for writing checkpointing data to a computer having a standby virtual machine for each checkpointed component on a computer having an active virtual machine. In one embodiment, the checkpointing data is processed on a per virtual machine basis. This is performed in a way that allows checkpointing data packets from multiple sources to be transferred asynchronously, subsequently reassembled into a coherent checkpoint message, and applied asynchronously.

Abstract: An apparatus and method for fault-tolerant and spread spectrum clocking. In one embodiment a master clock synthesizer circuit generates an output clock signal of varying frequency within a predetermined range of frequencies. A slave clock synthesizer circuit is provided to track the output clock signal generated by the master clock synthesizer circuit. If the master clock synthesizer circuit fails or generates an invalid output clock signal, the slave clock synthesizer circuit takes over and functions as the master clock synthesizer circuit. In one embodiment a method of fault-tolerant spread spectrum clocking includes generating a first digital data stream; receiving the first digital data stream, a first input reference signal and a first clock signal in a master clock synthesizer circuit; generating an first output clock signal of varying frequency by the master clock synthesizer circuit in response to the first digital data stream and the first clock signal.

Abstract: A transparent high-availability solution utilizing virtualization technology is presented. A cluster environment and management thereof is implemented through an automated installation and setup procedure resulting in a cluster acting as a single system. The cluster is setup in an isolated virtual machine on each of a number of physical nodes of the system. Customer applications are run within separate application virtual machines on one physical node at a time and are run independently and unaware of their configuration as part of a high-availability cluster. Upon detection of a failure, traffic is rerouted through a redundant node and the application virtual machines are migrated from the failing node to another node using live migration techniques.

Abstract: A method for dynamically determining a predetermined previous condition of a rule-based system comprising a plurality of rules. Each of the plurality of rules is associated with a transaction and a condition under which the transaction is executed. In one embodiment, the method includes the steps of (a) determining a system condition; (b) determining an immediate previous condition that caused the system condition; (c) setting the immediate previous condition to the system condition; and (d) repeating steps (b) and (c) until the predetermined previous condition is reached.

Abstract: A system is provided for rapidly synchronizing two or more processing elements in a fault-tolerant computing system. Embodiments of this system allow for the rapid synchronization of two processing elements through partial copies of the contents of memory associate with each processing element.

Abstract: An apparatus and method for fault-tolerant and spread spectrum clocking. In one embodiment a master clock synthesizer circuit generates an output clock signal of varying frequency within a predetermined range of frequencies. A slave clock synthesizer circuit is provided to track the output clock signal generated by the master clock synthesizer circuit. If the master clock synthesizer circuit fails or generates an invalid output clock signal, the slave clock synthesizer circuit takes over and functions as the master clock synthesizer circuit. In one embodiment a method of fault-tolerant spread spectrum clocking includes generating a first digital data stream; receiving the first digital data stream, a first input reference signal and a first clock signal in a master clock synthesizer circuit; generating an first output clock signal of varying frequency by the master clock synthesizer circuit in response to the first digital data stream and the first clock signal.

Abstract: A transparent high-availability solution utilizing virtualization technology is presented. A cluster environment and management thereof is implemented through an automated installation and setup procedure resulting in a cluster acting as a single system. The cluster is setup in an isolated virtual machine on each of a number of physical nodes of the system. Customer applications are run within separate application virtual machines on one physical node at a time and are run independently and unaware of their configuration as part of a high-availability cluster. Upon detection of a failure, traffic is rerouted through a redundant node and the application virtual machines are migrated from the failing node to another node using live migration techniques.

Abstract: A method of automatically determining firing priority in a plurality of rules. The method includes the steps of determining a level of dependency of each rule; and generating a hierarchy of rules in response to the level of dependency of each rule, wherein the firing priority corresponds to the hierarchy of rules. In another embodiment, the method further includes the step of determining if the hierarchy results in an inconsistency. In another embodiment, the method further comprises the step of determining if the hierarchy results in a loop. In yet another embodiment, the step of determining a level of dependency of each rule is performed in response to an initial event. In one embodiment the method includes the step of determining if there are reciprocal dependencies between any two rules in the set of rules.

Abstract: A method for tracking modified pages is provided. The method is utilized in a fault-tolerant system, the fault-tolerant system comprising a first computer system and a second computer system. The method involves copying a memory from the first computer system to the second computer system at a first point in time. Between the first point in time and a second point in time, a scheduler tracks processes that execute on the first computer system in a harvest list. After the second point in time, the processes that made changes to the memory between the first and second points in time are retrieved. The changes to the memory are then copied to the second computer system and the changes are applied to the memory of the second computer system.

Abstract: Methods and systems are provided by which a computer system, and in particular, a lockstep fault-tolerant computer system, may be split into a plurality of independently operational subsystems. Each subsystem may be examined, managed or upgraded by an administrator while the overall computer system continues to service end-users. Finally, the separate subsystems may be merged in an efficient fashion and fault-tolerant operation will resume upon the combined system.

Abstract: A method of automatically determining firing priority in a plurality of rules. The method includes the steps of determining a level of dependency of each rule; and generating a hierarchy of rules in response to the level of dependency of each rule, wherein the firing priority corresponds to the hierarchy of rules. In another embodiment, the method further includes the step of determining if the hierarchy results in an inconsistency. In another embodiment, the method further comprises the step of determining if the hierarchy results in a loop. In yet another embodiment, the step of determining a level of dependency of each rule is performed in response to an initial event.

Abstract: A transparent high-availability solution utilizing virtualization technology is presented. A cluster environment and management thereof is implemented through an automated installation and setup procedure resulting in a cluster acting as a single system. The cluster is setup in an isolated virtual machine on each of a number of physical nodes of the system. Customer applications are run within separate application virtual machines on one physical node at a time and are run independently and unaware of their configuration as part of a high-availability cluster. Upon detection of a failure, traffic is rerouted through a redundant node and the application virtual machines are migrated from the failing node to another node using live migration techniques.

Abstract: An apparatus and method for fault-tolerant and spread spectrum clocking. In one embodiment a master clock synthesizer circuit generates an output clock signal of varying frequency within a predetermined range of frequencies. A slave clock synthesizer circuit is provided to track the output clock signal generated by the master clock synthesizer circuit. If the master clock synthesizer circuit fails or generates an invalid output clock signal, the slave clock synthesizer circuit takes over and functions as the master clock synthesizer circuit. In one embodiment a method of fault-tolerant spread spectrum clocking includes generating a first digital data stream; receiving the first digital data stream, a first input reference signal and a first clock signal in a master clock synthesizer circuit; generating an first output clock signal of varying frequency by the master clock synthesizer circuit in response to the first digital data stream and the first clock signal.

Abstract: The invention relates to checkpointing memory. In one aspect, a processor directs a write request to a location within a first memory. The write request includes at least a data payload and an address identifying the location. An inspection module identifies the write request before it reaches the first memory, copies at least the address identifying the location, and forwards the write request to a memory agent within the first memory.

Abstract: A system is provided for rapidly synchronizing two or more processing elements in a fault-tolerant computing system. Embodiments of this system allow for the rapid synchronization of two processing elements through partial copies of the contents of memory associate with each processing element.

Abstract: A system is provided for rapidly synchronizing two or more processing elements in a fault-tolerant computing system. Embodiments of this system allow for the rapid synchronization of two processing elements through partial copies of the contents of memory associate with each processing element.

Abstract: A system is provided for rapidly synchronizing two or more processing elements in a fault-tolerant computing system. Embodiments of this system allow for the rapid synchronization of two processing elements through partial copies of the contents of memory associate with each processing element.

Abstract: An improved method and apparatus is provided for checkpointing and rollback of network operations. In one embodiment the method includes varying the checkpoint interval in response to a packet deferred timer and buffering data packets that would affect the states of other network devices in a deferred packets queue. The method further generates an outbound packet for transmission to a remote system, buffers the outbound packet until one of a checkpoint or rollback condition is met and varies a checkpoint interval in response to network load. In another embodiment the apparatus includes a transmitter to send an outgoing packet to a remote system, a deferred transmit queue connected to the transmitter and a deferred packet timer that is configured to vary a checkpoint interval based on a predetermined value.

Abstract: An apparatus and method is provided for translating addresses and rerouting them to preferably one of at least two destinations. This is accomplished through the use of a memory unit and a combination of logic operation units that essentially operate as a look-up translation table configurable by software. The apparatus includes an input to receive an address of a certain length and a memory unit that is adapted to receive a portion of the input address and output another address of a predetermined length which is mapped to the input. The method includes receiving input addresses of a certain length and performing an operation on a portion of the input address to determine its destination.

Abstract: Methods and systems are provided by which a computer system, and in particular, a lockstep fault-tolerant computer system, may be split into a plurality of independently operational subsystems. Each subsystem may be examined, managed or upgraded by an administrator while the overall computer system continues to service end-users. Finally, the separate subsystems may be merged in an efficient fashion and fault-tolerant operation will resume upon the combined system.