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Redundancy Features

The system has the following redundancy features:

SRP Modules

The SRP module uses a 1:1 redundancy scheme. When two SRP modules of the same type are installed in the system chassis, one acts as a primary and the second as a standby. Both SRP modules share a single SRP I/O module located in the rear of the chassis. If the primary SRP fails, the redundant SRP module assumes control without rebooting or initializing. (As a consequence, if you upgrade software, you must copy the software to the redundant SRP and reboot it.) For information about configuring and managing SRP module redundancy, see ERX System Basics Configuration Guide, Chapter 5, Managing Line Modules and SRP Modules.

After you install two SRP modules, the modules negotiate for the primary role. A number of factors determine which module becomes the primary; however, preference is given to the module in the lower-numbered slot. The SRP modules record their latest roles and retain them the next time you switch on the system. For information about installing SRP modules, see Chapter 3, Installing ERX Modules.

NVS Cards

If you have two SRP modules installed in a system, you can use NVS cards of different capacities on the SRP modules. The effective capacity of the higher-capacity NVS card will equal that of the lower-capacity NVS card. For information about installing NVS cards, see Chapter 3, Installing ERX Modules.

When you install new NVS cards or SRP modules, you must issue the synchronize command to match the file system of the NVS card on the redundant SRP module with the file system of the NVS card on the primary SRP module. (The NVS card on the redundant SRP module will hereafter be referred to as the redundant NVS card; the NVS card on the primary SRP module will hereafter be referred to as the primary NVS card.)

If the capacity of the primary NVS card is equal to or smaller than that of the redundant NVS card, the system copies all the files from the primary NVS card to the redundant NVS card. However, if the capacity of the primary NVS card exceeds that of the redundant NVS card, the system creates an invisible synchronization reserve file on the primary NVS card, provided that there is enough space for the file.

The purpose of the synchronization file is to prevent the creation of data that will not fit on the redundant NVS card. The file contains no useful data, and is not visible when you view the files in NVS. The size of the file is equal to the difference in capacities of the two NVS cards. For example, if the primary NVS card has a capacity of 224 MB, and the redundant NVS card has a capacity of 220 MB, the size of the synchronization file is 4 MB, and only 220 MB of space is available on the primary NVS card.

If there is not enough space on the primary NVS card to create the synchronization reserve file, the synchronize command fails, and you see a warning message on the console. To resolve this issue, either delete unwanted files from the primary NVS card or replace the redundant NVS card with a higher-capacity NVS card.

Line Modules

The ERX system supports line module redundancy for several line modules. For details about which line modules support redundancy, see Appendix 10, Module Specifications. In this scheme, an extra line access module in a group of identical line modules provides redundancy in case of line module failure. To use this feature, you need a:

A redundancy midplane may cover 2-6 slots. It provides additional connectivity that enables the spare line module to assume control of the I/O module associated with any failed line module in the redundancy group. The spare I/O module provides connectivity from the spare line module to the redundancy midplane.

The process by which the system switches to the spare line module is called switchover. When switchover occurs, the system:

  1. Breaks the connection between the primary I/O module and the primary line module.
  2. Connects the primary I/O module to the spare line module via the redundancy midplane and redundancy I/O module.

Protocol processing then takes place on the spare line module.

Figure 1-10 shows the data flow when a spare line module becomes active.


Figure 1-10 Data flow when a spare line module is active

For information about installing modules for line module redundancy, see Chapter 3, Installing ERX Modules. For information about configuring and managing SRP module redundancy, see ERX System Basics Configuration Guide, Chapter 5, Managing Line Modules and SRP Modules, for more information.

Power

The system provides a power architecture that distributes redundant -48 VDC feeds through the system to each line module, SRP module, and fan module where DC-to-DC converters provide local conversion to the required secondary voltages. The system design prevents a failure of any one of the power components from causing any other component in the system to fail.

Fans

Forced air-cooling keeps the temperature of the ERX modules and components within normal operating limits. In the ERX-1400 series, six cooling fans are located in a tray at the top of the system (see Figure 7-8). In the ERX-700 series, four cooling fans are located in a tray on one side of the system (see Figure 7-9).

The system monitors the temperature of each module. If the temperature of a module exceeds the maximum limit, the system immediately goes into thermal protection mode. In this mode, the modules consume extremely low levels of power. For information about troubleshooting high operating temperatures, see Chapter 8, Troubleshooting.

The fan tray has two redundant converters that power the fans (for the ERX-1400 series, a -24 V, 50 W converter; for the ERX-700 series, a -12 V, 15 W converter). If one converter fails, the other takes over. In addition, the system software reports an alarm if any of the fans overrotate or underrotate or if one of the converters fails.


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