Juniper Networks ERX Hardware 8 - Manual (Page 35)

ERX Overview
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 “Installing Modules” on page 35.
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 “Installing Modules” on page 35.
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
cannot 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 the primary NVS card does not have enough space to create the synchronization
reserve file, the synchronize command fails, and a warning message is displayed
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
NOTE: This section applies to ERX-7xx and ERX-14xx models only. ERX-310 routers
do not offer line module redundancy.
ERX-7xx and ERX-14xx models support line module redundancy for several
line modules. For details about which line modules support redundancy,
see the ERX Module Guide. In this scheme, an extra line module in a group
Redundancy Features 17