Technical Reference Guide

Managing MTBF Statistics
Express5800/320Ma System Features 2-5
MTBF Calculation
The calculation of the new the MTBF is as follows:
For the MTBF to be below the threshold, the FailureCount must be equal to or greater
than 3, and the calculated the MTBF must be below the threshold. For example,
Table 2-2 shows the progression of failures causing recalculation of the MTBF. The
MTBF threshold in this example is 600, so the device is removed from service when
the new MTBF is less than 600, or 517 in the example.
Displaying MTBF Information
To display the current MTBF information for a device in the details pane, you can select
the device in the console tree of ftSMC. The following example shows the time of the
last fault, the MTBF Threshold, the number of faults, and the current MTBF value.
MTBF: Type Use Threshold
MTBF: TimeOfLastFault May 30, 2004 15:07:24
MTBF: Threshold 300 seconds
MTBF: NumberOfFaults 2
MTBF: Current 532220 seconds
An out-of-service hardware device remains out of service until you clear the MTBF or
change the MTBF threshold. Inserting a new device clears the MTBF.
A value of 0 (Unknown) for MTBF: Current indicates that the device has not failed
enough times to be able to calculate the MTBF.
Table 2-2. Example MTBF Calculation
Current MTBF Failure Count Time Since Last Failure New MTBF
1000 3 500 833
833 4 300 700
700 5 200 600
600 6 100 517
CurrentMtbf * (FailureCount - 1) + TimeSinceLastFailure
MTBF =
FailureCount