Patent Number: 
Section: claims

1. A method for monitoring the health of a computer system, comprising:receiving a variance of a time series for a monitored telemetry variable within the computer system,calculating a residual function of the variance of the time series for the monitored telemetry variable;calculating a first-difference function of the variance of the time series from the residual function;determining whether the first-difference function indicates that the computer system is at the onset of degradation; andif so, performing a remedial action. 2. The method of claim 1, wherein prior to receiving the variance for the time series for the monitored telemetry variable, the method further comprises:receiving the time series for the monitored telemetry variable; andcalculating the variance of the time series for the monitored telemetry variable. 3. The method of claim 1, wherein calculating the first-difference function of the time series involves, for each time point within the time series, subtracting a value of the time series at a previous time point from the value of the time series at a present time point. 4. The method of claim 3, further comprises dividing the result of the subtraction by the value of a length of a time interval between the previous time point and the present time point. 5. The method of claim 1, wherein calculating the residual function for a time series involves:for each time interval in the time series,calculating a running average of values for the time series up to and including a present time interval; andsubtracting the running average from a value of the time series at the present time interval. 6. The method of claim 1, wherein determining whether the first-difference function indicates that the computer system is at the onset of degradation involves determining whether the first-difference function exceeds a specified threshold. 7. The method of claim 1, wherein determining whether the first-difference function indicates that the computer system is at the onset of degradation involves:performing a Sequential Probability Ratio Test (SPRT) on the first-difference function; anddetermining whether the SPRT generates an alarm. 8. The method of claim 7, wherein the SPRT can include one or more of:a positive variance first-difference test, which generates an alarm if the first-difference function for the variance of the time series for the monitored telemetry variable is increasing; anda negative variance first-difference test, which generates an alarm if the first-difference function for the variance of the time series for the monitored telemetry variable is decreasing. 9. The method of claim 1, wherein performing the remedial action can involve performing one or more of:recording a time when the onset of degradation occurred;notifying a system administrator that the computer system is at the onset of degradation;shutting down the computer system;backing up data stored on the computer system;failing-over to a redundant computer system; andreplacing one or more components which are at the onset of degradation. 10. A computer-readable storage medium storing instructions that when executed by a computer cause the computer to perform a method for monitoring the health of a computer system, wherein the method comprises:receiving a variance of a time series for a monitored telemetry variable within the computer system;calculating a residual function of the variance of the time series for the monitored telemetry variable;calculating a first-difference function of the variance of the time series from the residual function;determining whether the first-difference function indicates that the computer system is at the onset of degradation; andif so, performing a remedial action. 11. The computer-readable storage medium of claim 10, prior to receiving the variance for the time series for the monitored telemetry variable, the method further comprises:receiving the time series for the monitored telemetry variable; andcalculating the variance of the time series for the monitored telemetry variable. 12. The computer-readable storage medium of claim 10, wherein calculating the first-difference function of the time series involves, for each time point within the time series, subtracting a value of the time series at a previous time point from the value of the time series at a present time point. 13. The computer-readable storage medium of claim 12, wherein the method further comprises dividing the result of the subtraction by the value of a length of a time interval between the previous time point and the present time point. 14. The computer-readable storage medium of claim 10, wherein calculating the residual function for a time series involves:for each time interval in the time series,calculating a running average of values for the time series up to and including a present time interval; andsubtracting the running average from a value of the time series at the present time interval. 15. The computer-readable storage medium of claim 10, wherein determining whether the first-difference function indicates that the computer system is at the onset of degradation involves determining whether the first-difference function exceeds a specified threshold. 16. The computer-readable storage medium of claim 10, wherein determining whether the first-difference function indicates that the computer system is at the onset of degradation involves:performing a Sequential Probability Ratio Test (SPRT) on the first-difference function; anddetermining whether the SPRT generates an alarm. 17. The computer-readable storage medium of claim 16, wherein the SPRT can include one or more of:a positive variance first-difference test, which generates an alarm if the first-difference function for the variance of the time series for the monitored telemetry variable is increasing; anda negative variance first-difference test, which generates an alarm if the first-difference function for the variance of the time series for the monitored telemetry variable is decreasing. 18. The computer-readable storage medium of claim 10, wherein performing the remedial action can involve performing one or more of:recording a time when the onset of degradation occurred;notifying a system administrator that the computer system is at the onset of degradation;shutting down the computer system;backing up data stored on the computer system;failing-over to a redundant computer system; andreplacing one or more components which are at the onset of degradation. 19. An apparatus that monitors the health of a computer system, comprising:a receiving mechanism configured to receive a variance of a time series for a monitored telemetry variable within the computer system,a residual-calculation mechanism configured to calculate a residual function of the variance of the time series for the monitored telemetry variable;a difference-calculation mechanism configured to calculate a first-difference function of the variance of the time series from the residual function;a degradation-detection mechanism configured to determine whether the first-difference function indicates that the computer system is at the onset of degradation; anda remedial-action mechanism, wherein if the degradation-detection mechanism determines that the computer system is at the onset of degradation, the remedial-action mechanism is configured to perform a remedial action.