Spares Planning

This appendix explains how to calculate a suggested number of spare cards and other components for the Cisco ICS 7750. It includes the following sections:

To reduce the length of system outages caused by hardware or media failures, Cisco recommends that you set inventory targets for mission-critical cards and other components. Spares planning can mean the difference between meeting or not meeting system reliability goals.

Spares planning is based on the following metrics and assumptions:

Number (N). The quantity of installed components (such as a particular card) that are serviced by the same organization (such as a repair depot).
Failure rate (F). The estimated number of failures for a particular component during one million hours of operation.
Turnaround time for repair (T). The amount of time required to repair or replace a particular component that has failed.
Sparing interval. The amount of time that spares should last before being replenished. The sparing interval is assumed to be one year following the installation of the system.
Card ambient temperature. The average temperature of the air immediately surrounding a card (typically higher than the ambient room temperature). Card failure rates are based on a card ambient temperature of 40°C (104°F).

Calculating Spares Requirements

Complete the following steps to calculate the number of spares for a particular component:

Step 1 Count the number (N) of components that are in service.

Step 2 Contact your Cisco sales representative for information about the failure rate (F) (expressed in terms of failures per million hours of operation) for the component.

Step 3 Determine the turnaround time (T) in hours.

Step 4 Multiply N x F x T. The result is the NFT value.

Step 5 Find the NFT value in the first column of Table B-1 and locate the corresponding number of spares in the second column.

NFT Values

Table B-1 lists the number of spares required for a particular NFT value:

Table B-1: NFT-to-Number of Spares Translation
NFT Values
Number of

From
To
Spares

0

0.001

1

0.001

0.0452

2

0.0452

0.189

3

0.189

0.425

4

0.425

0.734

5

0.734

1.09

6

1.09

1.5

7

1.5

1.95

8

1.95

2.43

9

2.43

2.94

10

NFT Values		Number of
From	To	Spares
0	0.001	1
0.001	0.0452	2
0.0452	0.189	3
0.189	0.425	4
0.425	0.734	5
0.734	1.09	6
1.09	1.5	7
1.5	1.95	8
1.95	2.43	9
2.43	2.94	10

Table of Contents

Spares Planning

Spares Planning

Overview

Calculating Spares Requirements

NFT Values